U.S. patent application number 13/760201 was filed with the patent office on 2013-08-08 for rf transceiver with distributed filtering topology.
This patent application is currently assigned to RF MICRO DEVICES, INC.. The applicant listed for this patent is RF MICRO DEVICES, INC.. Invention is credited to Ruediger Bauder, Marcus Granger-Jones, Nadim Khlat.
Application Number | 20130201881 13/760201 |
Document ID | / |
Family ID | 48902809 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130201881 |
Kind Code |
A1 |
Bauder; Ruediger ; et
al. |
August 8, 2013 |
RF TRANSCEIVER WITH DISTRIBUTED FILTERING TOPOLOGY
Abstract
This disclosure includes embodiments of a radio frequency (RF)
transceiver having a distributed duplex filtering topology. The RF
transceiver includes a power amplifier and a tunable RF duplexer.
The tunable RF duplexer is configured to input an RF transmission
input signal from the power amplifier, generate an RF transmission
output signal that operates within an RF transmission band in
response to the RF transmission input signal from the power
amplifier, and simultaneously output the RF transmission output
signal to an antenna and input an RF receive input signal that
operates within an RF receive band from the antenna. The power
amplifier includes a plurality of RF amplifier stages coupled in
cascode and an RF filter coupled between a first one of the RF
amplifier stages and a second one of the RF amplifier stages.
Accordingly, the RF filter is configured to provide tuning within
the RF receive band.
Inventors: |
Bauder; Ruediger;
(Feldkirchen-Westerham, DE) ; Granger-Jones; Marcus;
(Scotts Valley, CA) ; Khlat; Nadim; (Cugnaux,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RF MICRO DEVICES, INC.; |
Greensboro |
NC |
US |
|
|
Assignee: |
RF MICRO DEVICES, INC.
Greensboro
NC
|
Family ID: |
48902809 |
Appl. No.: |
13/760201 |
Filed: |
February 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61595795 |
Feb 7, 2012 |
|
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Current U.S.
Class: |
370/277 |
Current CPC
Class: |
H04B 1/525 20130101;
H04L 25/03878 20130101; H03H 7/48 20130101; H04L 5/14 20130101;
H04B 1/44 20130101 |
Class at
Publication: |
370/277 |
International
Class: |
H04L 5/14 20060101
H04L005/14 |
Claims
1. A radio frequency (RF) transceiver having a distributed duplex
filtering topology comprising: a power amplifier comprising a
plurality of RF amplifier stages coupled in cascode and an RF
filter coupled between a first one of the plurality of RF amplifier
stages and a second one of the plurality of RF amplifier stages,
wherein: each of the plurality of RF amplifier stages is configured
to amplify an RF transmission input signal that operates within an
RF transmission band of an RF communication band; and the RF filter
has a frequency response that defines a stopband and is tunable to
provide the stopband within an RF receive band of the RF
communication band; and a tunable RF duplexer configured to input
the RF transmission input signal from the power amplifier, generate
an RF transmission output signal that operates within the RF
transmission band in response to the RF transmission input signal
from the power amplifier, and simultaneously output the RF
transmission output signal to an antenna and input an RF receive
input signal that operates within the RF receive band from the
antenna.
2. The RF transceiver of claim 1 further comprising a low noise
amplifier (LNA) wherein: the tunable RF duplexer is further
configured to generate an RF receive output signal that operates
within the RF receive band in response to the RF receive input
signal from the antenna; and the LNA comprises a linear
amplification stage and a tunable high-selectivity bandpass filter;
wherein: the linear amplification stage is coupled to receive the
RF receive output signal from the tunable RF duplexer, and is
configured to amplify the RF receive output signal; and the tunable
high-selectivity bandpass filter is tunable to provide a passband
within the RF receive band, and is coupled to receive the RF
receive output signal after amplification by the linear
amplification stage.
3. The RF transceiver of claim 2 wherein the LNA further comprises
a translational filter, the translational filter being coupled to
receive the RF receive output signal that is output from the
tunable high-selectivity bandpass filter.
4. The RF transceiver of claim 3 wherein the translational filter
comprises an intermediate frequency (IF) filter, wherein the
translational filter is configured to translate a frequency
response of the IF filter having a passband at an IF into an RF
frequency response with a translated passband within the RF receive
band.
5. The RF transceiver of claim 4 wherein the translational filter
further comprises an RF passive mixer configured to mix the RF
receive output signal with a local oscillator signal.
6. The RF transceiver of claim 2 wherein the linear amplification
stage is configured to receive the RF receive output signal as a
single-ended signal and output the RF receive output signal as a
differential signal.
7. The RF transceiver of claim 2 wherein the tunable RF duplexer
comprises: a first hybrid coupler operable to: split the RF
transmission input signal into a first RF quadrature hybrid
transmission signal (QHTS) and a second RF QHTS; split the RF
receive input signal into a first RF quadrature hybrid receive
signal (QHRS) and a second RF QHRS; and combine the first RF QHTS
and the second RF QHTS into the RF transmission output signal when
reflected back to the first hybrid coupler; a second hybrid coupler
configured to combine the first RF QHRS and the second RF QHRS into
the RF receive output signal; and an RF filter circuit that is
tunable so as to pass the first RF QHRS and the second RF QHRS to
the second hybrid coupler and to reflect the first RF QHTS and the
second RF QHTS back to the first hybrid coupler.
8. The RF transceiver of claim 1 wherein the tunable RF duplexer
comprises: a first hybrid coupler operable to: split the RF
transmission input signal into a first RF quadrature hybrid
transmission signal (QHTS) and a second RF QHTS; split the RF
receive input signal into a first RF quadrature hybrid receive
signal (QHRS) and a second RF QHRS; and combine the first RF QHTS
and the second RF QHTS into the RF transmission output signal when
reflected back to the first hybrid coupler; a second hybrid coupler
configured to combine the first RF QHRS and the second RF QHRS into
an RF receive output signal; and an RF filter circuit that is
tunable so as to pass the first RF QHRS and the second RF QHRS to
the second hybrid coupler and to reflect the first RF QHTS and the
second RF QHTS back to the first hybrid coupler.
9. The tunable RF duplexer of claim 8 further comprising a tuning
circuit wherein: the RF filter circuit has a frequency response
that defines a passband; the RF filter circuit is tunable to shift
the passband; and the tuning circuit is configured to tune the
frequency response so that a signal bandwidth of the first RF QHRS
and a signal bandwidth of the second RF QHRS are each within the
passband.
10. The tunable RF duplexer of claim 8 further comprising a tuning
circuit wherein: the RF filter circuit has a frequency response
that defines a stopband; the RF filter circuit is tunable to shift
the stopband; and the tuning circuit is configured to tune the
frequency response so that a signal bandwidth of the first RF QHTS
and a signal bandwidth of the second RF QHTS are each within the
stopband.
11. The tunable RF duplexer of claim 8 further comprising a tuning
circuit wherein: the RF filter circuit has a frequency response
that defines a passband and a stopband; the RF filter circuit is
tunable to shift the passband and shift the stopband; and the
tuning circuit is configured to tune the frequency response so as
to shift the passband so that a signal bandwidth of the first RF
QHRS and a signal bandwidth of the second RF QHRS are each within
the passband, and to shift the stopband so that a signal bandwidth
of the first RF QHTS and a signal bandwidth of the second RF QHTS
are each within the stopband.
12. The tunable RF duplexer of claim 8 wherein the RF filter
circuit comprises a first RF filter and a second RF filter and
wherein: the first RF filter is connected between the first hybrid
coupler and the second hybrid coupler and is operable to reflect
the first RF QHTS back to the first hybrid coupler and to pass the
second RF QHRS to the second hybrid coupler; and the second RF
filter is connected between the first hybrid coupler and the second
hybrid coupler and is operable to reflect the second RF QHTS back
to the first hybrid coupler and pass the first RF QHRS to the
second hybrid coupler.
13. The tunable RF duplexer of claim 12 wherein the first RF filter
comprises: a series LC resonator coupled in shunt between the first
hybrid coupler and the second hybrid coupler, the series LC
resonator having a series resonant frequency; and a variable
capacitive element having a variable capacitance, the variable
capacitive element being coupled in shunt between the first hybrid
coupler and the second hybrid coupler such that the series LC
resonator and the variable capacitive element have a parallel
resonant frequency.
14. The tunable RF duplexer of claim 13 wherein the second RF
filter is identical to the first RF filter.
15. The tunable RF duplexer of claim 12 wherein the first RF filter
comprises a plurality of Surface Acoustic Wave (SAW) resonators,
wherein one of the SAW resonators is configured to reflect the
second RF QHTS back to the first hybrid coupler and to pass the
first RF QHRS to the second hybrid coupler.
16. A radio frequency (RF) transceiver having a distributed duplex
filtering topology comprising: a tunable RF duplexer configured to
input an RF receive input signal that operates within an RF receive
band of an RF communication band from an antenna, generate an RF
receive output signal that operates within the RF receive band in
response to the RF receive input signal from the antenna, and
simultaneously output an RF transmission output signal that
operates within an RF transmission band of the RF communication
band to the antenna and input the RF receive input signal from the
antenna; a low noise amplifier (LNA) comprising a linear
amplification stage and a tunable high-selectivity bandpass filter,
wherein: the linear amplification stage is coupled to receive the
RF receive output signal from the tunable RF duplexer, and is
configured to amplify the RF receive output signal; and the tunable
high-selectivity bandpass filter is tunable to provide a passband
within the RF receive band, and is coupled to receive the RF
receive output signal after amplification by the linear
amplification stage.
17. The RF transceiver of claim 16 wherein the LNA further
comprises a translational filter, the translational filter being
coupled to receive the RF receive output signal that is output from
the tunable high-selectivity bandpass filter.
18. The RF transceiver of claim 17 wherein the translational filter
comprises an intermediate frequency (IF) filter, wherein the
translational filter is configured to translate a frequency
response of the intermediate frequency (IF) filter having a
passband at an IF into an RF frequency response with a translated
passband within the RF receive band.
19. The RF transceiver of claim 18 wherein the translational filter
further comprises an RF passive mixer configured to mix the RF
receive output signal with a local oscillator signal.
20. The RF transceiver of claim 16 wherein the linear amplification
stage is configured to receive the RF receive output signal as a
single-ended signal and output the RF receive output signal as a
differential signal.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/595,795, filed on Feb. 7, 2012 and
entitled "TUNABLE DUPLEXER," the disclosure of which is hereby
incorporated herein by reference in its entirety.
[0002] The application is also related to U.S. patent application
Ser. No. 13/633,459, filed on Oct. 2, 2012 and entitled "TUNABLE
DUPLEXER ARCHITECTURE," which claims the benefit of U.S.
provisional patent application No. 61/542,939, filed on Oct. 4,
2011 and entitled "TUNABLE DUPLEXER ARCHITECTURE," the disclosures
of which are hereby incorporated herein by reference in their
entireties.
FIELD OF THE DISCLOSURE
[0003] This disclosure relates generally to radio frequency (RF)
duplexers and duplexing methods related to RF front-end
modules.
BACKGROUND
[0004] A duplexer is a device that facilitates bi-directional
communication (i.e., simultaneous reception and emission) by a
common antenna. In order to facilitate simultaneous reception and
emission of signals over the antenna, the duplexer needs to be
designed for operation at both receive and transmission bands while
providing adequate isolation between receive and transmission
signals. To provide multi-mode and multi-band operation, radio
frequency (RF) duplexers often use multiple parallel duplexer
components selected using an ever-growing number of switches. As
such, this type of RF duplexer solution presents ever-increasing
demands with regard to cost and size.
[0005] Accordingly, more adaptable RF duplexers are needed to
provide multi-band/multi-mode operations that do not require
increases in cost and size.
SUMMARY
[0006] This disclosure includes embodiments of a radio frequency
(RF) transceiver having a distributed duplex filtering topology.
The RF transceiver includes a power amplifier and a tunable RF
duplexer. The tunable RF duplexer is configured to input an RF
transmission input signal from the power amplifier, generate an RF
transmission output signal that operates within an RF transmission
band in response to the RF transmission input signal from the power
amplifier, and simultaneously output the RF transmission output
signal to an antenna and input an RF receive input signal that
operates within an RF receive band from the antenna. The power
amplifier includes a plurality of RF amplifier stages coupled in
cascode and an RF filter coupled between a first one of the
plurality of RF amplifier stages and a second one of the plurality
of RF amplifier stages. Accordingly, the RF filter is configured to
provide tuning within the RF receive band.
[0007] Those skilled in the art will appreciate the scope of the
disclosure and realize additional aspects thereof after reading the
following detailed description in association with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The accompanying drawings incorporated in and forming a part
of this specification illustrate several aspects of the disclosure,
and together with the description serve to explain the principles
of the disclosure.
[0009] FIG. 1 illustrates one embodiment of a tunable radio
frequency (RF) duplexer.
[0010] FIG. 2 illustrates exemplary procedures that may be
implemented by the tunable RF duplexer shown in FIG. 1 so that the
tunable RF duplexer may simultaneously receive an RF receive input
signal from an upstream receive chain while transmitting an RF
transmission output signal to an antenna, and may receive an RF
transmission input signal from a downstream transmission chain
while providing an RF transmission output signal to the same
antenna.
[0011] FIG. 2A is a frequency domain representation of one
embodiment of an RF transmission input signal that operates within
an RF transmission band and an RF receive output signal that
operates within an RF receive band.
[0012] FIG. 2B is a frequency domain representation of a frequency
response as S21 and S12 parameters provided by an RF filter circuit
in the tunable RF duplexer shown in FIG. 1, wherein the frequency
response defines a passband and a stopband.
[0013] FIG. 2C illustrates the frequency response shown in FIG. 2B
after the passband has been shifted to include the RF receive band
shown in FIG. 2A and the stopband has been shifted to include the
RF transmission band shown in FIG. 2A.
[0014] FIG. 2D illustrates the frequency response of the RF filter
circuit as S11 and S22 parameters.
[0015] FIG. 2E is a frequency domain representation of one
embodiment of a first RF quadrature hybrid receive signal (QHRS)
provided by splitting the RF receive input signal, and a first RF
quadrature hybrid transmission signal (QHTS) provided by splitting
the RF transmission input signal.
[0016] FIG. 2F is a frequency domain representation of one
embodiment of a second RF QHRS provided by splitting the RF receive
input signal and a second RF QHTS provided by splitting the RF
transmission input signal.
[0017] FIG. 2G is a frequency domain representation of one
embodiment of the RF receive output signal provided as a result of
combining the first RF QHRS and the second RF QHRS and the RF
transmission output signal provided as a result of combining the
first RF QHTS and the second RF QHTS.
[0018] FIG. 3A illustrates one embodiment of a tunable RF duplexer
along with a receive signal flow.
[0019] FIG. 3B illustrates the same embodiment of the tunable RF
duplexer along with a transmission signal flow.
[0020] FIG. 4 illustrates one embodiment of a frequency response of
an RF filter circuit in the tunable RF duplexer shown in FIGS. 3A
and 3B wherein the frequency response defines a stopband and a
passband.
[0021] FIG. 5 illustrates another embodiment of a tunable RF
duplexer, wherein the tunable RF duplexer is designed for dual
carrier aggregation.
[0022] FIG. 6A illustrates the tunable RF duplexer shown in FIG. 5
along with a receive signal flow.
[0023] FIG. 6B illustrates the tunable RF duplexer shown in FIG. 5
along with a transmission signal flow.
[0024] FIG. 7 illustrates one embodiment of a frequency response of
an RF filter circuit in the tunable RF duplexer shown in FIGS. 6A
and 6B wherein the frequency response defines a stopband and a
passband.
[0025] FIG. 8A illustrates one embodiment of a tunable hybrid
coupler that may be provided in the tunable RF duplexer shown in
FIGS. 6A and 6B.
[0026] FIG. 8B illustrates one embodiment of the tunable hybrid
coupler shown in FIG. 8A formed in a semiconductor substrate.
[0027] FIG. 9A illustrates one embodiment of a tunable hybrid
coupler that may be provided in the tunable RF duplexer shown in
FIGS. 6A and 6B.
[0028] FIG. 9B illustrates one embodiment of the tunable hybrid
coupler shown in FIG. 9A formed in a semiconductor substrate.
[0029] FIGS. 10A-10E illustrate different embodiments of an RF
filter that may be used in the tunable RF duplexer shown in FIGS.
6A and 6B.
[0030] FIG. 11A illustrates an exemplary frequency response of any
one of the RF filters shown in FIGS. 10A-10E.
[0031] FIG. 11B illustrates an RF communication channel having an
RF receive band and an RF transmission band separated by a duplex
offset.
[0032] FIG. 12A illustrates one embodiment of a tunable RF duplexer
that is tunable to set the stopband within the RF transmission band
and to set the passband within the RF receive band whenever the RF
receive band is at a higher frequency range than the RF
transmission band.
[0033] FIG. 12B illustrates one embodiment of a tunable RF duplexer
that is tunable to set the stopband within the RF transmission band
and to set the passband within the RF receive band whenever the RF
receive band is at a higher frequency range than the RF
transmission band.
[0034] FIG. 12C illustrates one embodiment of a tunable RF duplexer
that is tunable to set the stopband within the RF transmission band
and to set the passband within the RF receive band whenever the RF
receive band is at a higher frequency range than the RF
transmission band.
[0035] FIG. 13A illustrates a transmission signal flow of the
tunable RF duplexer shown in FIG. 12C.
[0036] FIG. 13B illustrates a receive signal flow of the tunable RF
duplexer shown in FIG. 12C.
[0037] FIG. 14 illustrates one embodiment of an RF transceiver
having a distributed duplex filtering topology.
DETAILED DESCRIPTION
[0038] The embodiments set forth below represent the necessary
information to enable those skilled in the art to practice the
disclosure and illustrate the best mode of practicing the
disclosure. Upon reading the following description in light of the
accompanying drawings, those skilled in the art will understand the
concepts of the disclosure and will recognize applications of these
concepts not particularly addressed herein. It should be understood
that these concepts and applications fall within the scope of the
disclosure and the accompanying claims.
[0039] FIG. 1 illustrates an embodiment of a tunable radio
frequency (RF) duplexer 10. An antenna 12 is operably associated
with the tunable RF duplexer 10 and is capable of radiating RF
receive signals and absorbing radiated RF transmission signals. In
order to prevent out-of-band noise and spurious emissions from
distorting RF transmission and receive signals, the tunable RF
duplexer 10 provides isolation between RF receive signals and RF
transmission signals, as well as out-of-band filtering.
Accordingly, the tunable RF duplexer 10 allows for an RF receive
input signal 14 to be intercepted by the antenna 12 while
simultaneously emitting an RF transmission output signal 16 from
the antenna 12.
[0040] In this embodiment, the tunable RF duplexer 10 includes a
first hybrid coupler 18, a second hybrid coupler 20, an RF filter
circuit 22, and a tuning circuit 24. The RF filter circuit 22
includes an RF filter 23A across its bottom ports and an RF filter
23B across its top ports. Thus, the RF filter circuit 22 is a
four-port network. However, the RF filter 23A and the RF filter 23B
are independent of one another and each of the RF filters 23A, 23B
operates as a two-port network. Also, the RF filter 23A and the RF
filter 23B may be identical, and thus may each have the same
individual frequency response.
[0041] The first hybrid coupler 18 is operable to receive an RF
transmission input signal 26 from upstream RF circuitry. For
example, the RF transmission input signal 26 is received from a
power amplifier 28 upstream from the tunable RF duplexer 10. The RF
transmission output signal 16 is provided by the first hybrid
coupler 18 at the antenna 12. An RF receive output signal 30 is
transmitted by the second hybrid coupler 20 to a low noise
amplifier (LNA) 31. Prior to the first hybrid coupler 18 receiving
the RF transmission input signal 26, the RF transmission input
signal 26 is filtered by a second RF filter circuit 32 to remove
spurious emissions. As explained in further detail below, the first
hybrid coupler 18, the RF filter circuit 22, and the second hybrid
coupler 20 provide the appropriate isolation between transmission
and receive.
[0042] FIG. 2 illustrates exemplary procedures that may be
implemented to provide RF duplexing. As explained in further detail
below, the procedures described in FIG. 2 are implemented by the
tunable RF duplexer 10 shown in FIG. 1. Different embodiments of
these exemplary procedures may be implemented depending on a
particular component structure of a tunable RF duplexer 10.
Furthermore, the order in which the procedures are presented is not
intended to imply a required sequence for the procedures. Rather,
the procedures may be implemented in a different sequence and/or
some or all of the procedures may be implemented
simultaneously.
[0043] As shown in FIG. 2, the tunable RF duplexer 10 receives the
RF transmission input signal 26 from an upstream transceiver chain
(procedure 1000). For example, the RF transmission input signal 26
is received by the tunable RF duplexer 10 from the power amplifier
28. The power amplifier 28 transfers power into the RF transmission
input signal 26 so that the RF transmission output signal 16 has a
sufficiently high spectral density for external propagation from
the antenna 12. Additionally, the tunable RF duplexer 10 receives
the RF receive input signal 14 (procedure 1002). The RF receive
input signal 14 was initially intercepted by the antenna 12.
[0044] FIG. 2A illustrates a graph of one embodiment of the RF
receive input signal 14 and the RF transmission input signal 26 in
the frequency domain. Both the RF receive input signal 14 and the
RF transmission input signal 26 operate in an RF communication band
34. In this embodiment, the RF communication band 34 is the set of
frequencies between a cutoff frequency C1 and a cutoff frequency
C2. Additionally, an RF receive band 36 and an RF transmission band
38 are defined within the RF communication band 34. The RF
transmission band 38 is defined as the set of frequencies between a
cutoff frequency f.sub.TB1 and a cutoff frequency f.sub.TB2.
Similarly, the RF receive band 36 is defined as the set of
frequencies between a cutoff frequency f.sub.RB1 and a cutoff
frequency f.sub.RB2. The RF receive input signal 14 operates in the
RF receive band 36 of the RF communication band 34.
[0045] In this example, a signal bandwidth 40 of the RF receive
input signal 14 is the set of frequencies that correspond to the
portion of the RF receive input signal 14 within 3 dB of a maximum
magnitude 42. The RF receive input signal 14 shown in FIG. 2A
operates at a frequency f.sub.R. This frequency f.sub.R corresponds
to the maximum magnitude 42 of the RF receive input signal 14. For
example, the frequency f.sub.R may be a carrier frequency of the RF
receive input signal 14. The signal bandwidth 40 reaches a cutoff
frequency f.sub.RBW1, since the frequency f.sub.RBW1 corresponds to
a value of the RF receive input signal 14 that is 3 dB from the
maximum magnitude 42. The signal bandwidth 40 also reaches a cutoff
frequency f because the cutoff frequency f.sub.RBW2 corresponds to
a value of the RF receive input signal 14 that is 3 dB from the
maximum magnitude 42.
[0046] With regard to the RF transmission input signal 26, the RF
transmission input signal 26 operates in the RF transmission band
38. More specifically, a signal bandwidth 43 of the RF transmission
input signal 26 is within the RF transmission band 38. A maximum
magnitude 44 of the RF transmission input signal 26 is placed at
the frequency f.sub.T. A cutoff frequency f.sub.TBW1 of the signal
bandwidth 43 corresponds to a value of the RF transmission input
signal 26 at 3 dB from the maximum magnitude 44. Similarly, a
cutoff frequency f.sub.TBW2 corresponds to a value of the RF
transmission input signal 26 that is 3 dB from the maximum
magnitude 44. The RF transmission input signal 26 may be said to
operate at the frequency f.sub.T since the frequency f.sub.T is a
carrier or a center frequency.
[0047] Portions of the RF receive input signal 14 and the RF
transmission input signal 26 outside of their respective signal
bandwidths 40, 43 may be considered spurious emissions. In other
words, the portions of the RF receive input signal 14 and the RF
transmission input signal 26 may be reduced or eliminated without
affecting the corresponding information or data in the RF
transmission input signal 26 and the RF receive input signal 14.
Spurious emissions include parasitic emissions, intermodulation,
interference, harmonic emissions, and frequency conversion
products. The signal bandwidth 40 and the signal bandwidth 43 are
defined as 3 dB bandwidths for pragmatic purposes. Generally
speaking, at least for the types of signals being shown in FIG. 2A,
the signal bandwidths 40, 43 are measured by finding 3 dB
magnitudes from the maximum magnitudes 42, 44, as explained above.
However, more accurately, a necessary signal bandwidth is an exact
amount of signal bandwidth required to carry the information or
data of a signal. Anything outside of this necessary bandwidth
would be considered spurious emissions. Thus, the signal bandwidth
40 and the signal bandwidth 43 may or may not include a small
portion of the spurious emissions. The necessary signal bandwidths
may be slightly smaller or slightly greater than the signal
bandwidths 40 and 43.
[0048] Finally, it should be noted that the RF receive input signal
14 and the RF transmission input signal 26 shown in FIG. 2A are
each narrow-band signals. Accordingly, the RF receive input signal
14 and the RF transmission input signal 26 may represent time
division multiplexing (TDM) signals, frequency division
multiplexing (FDM) signals, space division multiplexing (SDM)
signals, and/or the like. Accordingly, these narrow-band signals
may be said to operate at a particular frequency, which for the RF
receive input signal 14 is the frequency f.sub.R and for the RF
transmission input signal 26 is the frequency f.sub.T. The RF
receive band 36 is thus an RF receive channel within the RF
communication band 34, while the RF transmission band 38 is an RF
transmission channel within the RF communication band 34.
[0049] However, this disclosure is not limited to narrow-band
signals and the examples given in FIG. 2A and throughout this
disclosure are not intended to be limited in this manner. Rather,
embodiments of the tunable RF duplexer 10 and the method shown in
FIG. 2 may be provided for wide-band signals, and also for both
wide-band and narrow-band signals. With wide-band signals, such as
orthogonal frequency division multiple access (OFDMA) signals or
code division multiple access (CDMA) signals, information or data
is coded and spread across a larger portion of the spectrum. Thus,
there would be no signal with a single carrier frequency that has
all of the information or data, but rather there may be various
carriers carrying different coded portions of the information. As
such, the RF transmission band 38 for this type of RF transmission
input signal 26 may include various RF transmission channels.
Similarly, the RF receive band 36 may include various RF receive
channels. With CDMA signals and other wide-band spectrum signals,
it is more practical to define the bandwidths by simply using the
necessary bandwidth, as is known in the art.
[0050] FIG. 2B illustrates one embodiment of a frequency response
48 provided by the RF filter circuit 22. In FIG. 2B, the frequency
response 48 represents S21 and S12 parameters of each of the RF
filters 23A, 23B (shown in FIG. 1) individually, as a function of
frequency. Thus, the two-port S21 and S12 parameter of the RF
filter 23A is represented by the frequency response 48 in FIG. 2B.
Since the RF filter 23B is identical to the RF filter 23A, the
two-port S21 and S12 parameter of the RF filter 23B is also
represented by the frequency response 48 in FIG. 2B. The two-port
S21 and S12 parameter represents the forward and reverse
transmission of the RF filters 23A, 23B, as a function of
frequency. A passband 50 corresponds to S21/S12 values in the
frequency response 48 that are within 3 dB of a maxima 51. A
stopband 52 is determined relative to a minima 54. The maxima 51
and the minima 54 are set by the poles and zeros of the frequency
response 48. The stopband 52 is a set of frequencies that
correspond to S21/S12 values within 3 dB of the minima 54. In this
embodiment, the frequency response 48 defines the stopband 52 as a
notch. As explained in further detail below, the RF filter circuit
22 is tunable so as to shift the passband 50 and the stopband 52.
Thus, by tuning the RF filter circuit 22, the frequency response 48
may be transposed, so that the passband 50 and the stopband 52 are
provided at the desired frequency bands.
[0051] FIG. 2C illustrates the frequency response 48 once the
passband 50 is shifted to include the RF receive band 36, and once
the stopband 52 is shifted to include the RF transmission band 38.
As shown in FIG. 2C, the tuning circuit 24 tunes the passband 50 so
that the passband 50 includes the RF receive band 36 (procedure
1004). The tuning circuit 24 may also tune the stopband 52 so that
the stopband 52 includes the RF transmission band 38 (procedure
1006). In this manner, signals that operate in the RF receive band
36 are passed by the RF filter circuit 22, while signals that
operate in the RF transmission band 38 are blocked by the RF filter
circuit 22.
[0052] FIG. 2D illustrates the frequency response 48 once the
passband 50 is shifted to include the RF receive band 36, and once
the stopband 52 is shifted to include the RF transmission band 38.
However, in FIG. 2D, the frequency response 48 represents S11 and
S22 parameters of each of the RF filters 23A, 23B (shown in FIG. 1)
individually, as a function of frequency. Thus, the two-port S11
and S22 parameter of the RF filter 23A is represented by the
frequency response 48 in FIG. 2D. Since the RF filter 23B is
identical to the RF filter 23A, the two-port S11 and S22 parameter
of the RF filter 23B is also represented by the frequency response
48 in FIG. 2D. The two-port S11 and S22 parameter represents the
forward and reverse return loss of the RF filters 23A, 23B, as a
function of frequency. Note that in this embodiment, the S11/S22
values of the stopband 52 are at or near zero (0) dB in the RF
transmission band 38. By placing the stopband 52 at or near zero
(0) dB, reflections in the stopband 52 are maximized, while
insertion losses within the RF transmission band 38 are minimized.
Filtering thus removes noise outside of the RF transmission band 38
while minimizing losses of reflected signals.
[0053] Referring now to FIGS. 2E and 2F, the RF receive input
signal 14 is split into a first RF quadrature hybrid receive signal
(QHRS) 56 and a second RF QHRS 58 (procedure 1008). As such, the
first RF QHRS 56 is 90 degrees or .pi./2 radians out of phase with
the second RF QHRS 58. Also, the RF transmission input signal 26 is
also split into a first RF quadrature hybrid transmission signal
(QHTS) 60 and a second RF QHTS 62 (procedure 1010). FIGS. 2E and 2F
illustrate the first RF QHRS 56 and the second RF QHRS 58. The
first RF QHRS 56 and the second RF QHRS 58 have substantially
identical magnitude characteristics as the RF receive input signal
14. However, both the first RF QHRS 56 and the second RF QHRS 58
have a power spectral density that is at a power ratio with respect
to the power spectral density of the RF receive input signal 14. In
this example, the power ratio is 3 dB, and thus the first RF QHRS
56 and the second RF QHRS 58 have approximately one half of the
power of the RF receive input signal 14. The first RF QHRS 56 and
the second RF QHRS 58 are quadrature hybrids, since there is
approximately a 90-degree or .pi./2 radians phase difference
between the signals. As explained in further detail below, the
first hybrid coupler 18 (FIG. 1) splits the RF receive input signal
14 into the first RF QHRS 56 and the second RF QHRS 58.
[0054] Of course, non-ideal characteristics of the tunable RF
duplexer 10, such as parasitic impedances, may result in the first
RF QHRS 56 and the second RF QHRS 58 to be slightly unbalanced with
respect to one another, or to have slightly less than half the
power of the RF receive input signal 14. Also, non-ideal
characteristics can result in the phase difference between the
first RF QHRS 56 and the second RF QHRS 58 fluctuating somewhat
from a 90-degree or .pi./2 radians phase difference. These types of
errors are acceptable so long as the first RF QHRS 56 and the
second RF QHRS 58 can be combined into the RF receive output signal
30, such that the RF receive output signal 30 complies with
spectrum requirements for the RF communication band 34.
[0055] Again referring to FIG. 2 and FIGS. 2E and 2F, the first
hybrid coupler 18 (FIG. 1) splits the RF transmission input signal
26 into the first RF QHTS 60 and the second RF QHTS 62. Both the
first RF QHTS 60 and the second RF QHTS 62 have substantially
identical magnitude characteristics as the RF transmission input
signal 26. However, a spectral density of the first RF QHTS 60 and
the second RF QHTS 62 is at a power ratio with respect to a power
spectral density of the RF transmission input signal 26. In this
example, the power ratio is a 3 dB power ratio, and thus the first
RF QHTS 60 and the second RF QHTS 62 are at about half power with
respect to the RF transmission input signal 26. The first RF QHTS
60 and the second RF QHTS 62 are quadrature hybrids, because each
has a 90-degree or .pi./2 radians phase difference with respect to
the other. Non-ideal characteristics of the first hybrid coupler
18, such as parasitic impedances, may result in the first RF QHTS
60 and the second RF QHTS 62 having slightly lower power ratios
with respect to the RF transmission input signal 26. These
non-ideal characteristics may also result in the first RF QHTS 60
and the second RF QHTS 62 being slightly unbalanced. Furthermore,
the phase difference between the first RF QHTS 60 and the second RF
QHTS 62 may vary slightly due to non-ideal characteristics of the
tunable RF duplexer 10. These variations in both power and
magnitude are acceptable, so long as the first RF QHTS 60 and the
second RF QHTS 62 can combine into the RF transmission output
signal 16 and comply with spectral requirements for the RF
communication band 34.
[0056] Since the RF receive input signal 14 is split into the first
RF QHRS 56 and the second RF QHRS 58, both the first RF QHRS 56 and
the second RF QHRS 58 operate in the RF receive band 36 of the RF
communication band 34. As shown in FIGS. 2E and 2F, the frequency
response 48 of the RF filter circuit 22 has been transposed so that
the passband 50 and the stopband 52 are shifted into the RF
communication band 34. More particularly, the passband 50 is
shifted so that the RF receive band 36 is in the passband 50. When
the first hybrid coupler 18 outputs the first RF QHRS 56 and the
second RF QHRS 58, the RF filter circuit 22 filters the first RF
QHRS 56 and the second RF QHRS 58 to pass the first RF QHRS 56 and
the second RF QHRS 58 within the passband 50 (procedure 1012).
Since the first RF QHRS 56 and the second RF QHRS 58 are within the
passband 50, the RF filter circuit 22 is configured to pass the
first RF QHRS 56 and the second RF QHRS 58 to the second hybrid
coupler 20.
[0057] However, the stopband 52 has been shifted so that the RF
transmission band 38 is in the stopband 52. When the second hybrid
coupler 20 outputs the first RF QHTS 60 and the second RF QHTS 62,
the RF filter circuit 22 filters the first RF QHTS 60 and the
second RF QHTS 62 to reflect the first RF QHTS 60 and the second RF
QHTS 62 within the stopband 52 (procedure 1014). The first RF QHTS
60 and the second RF QHTS 62 operate within the RF transmission
band 38. Since the stopband 52 is in the RF transmission band 38,
the RF filter circuit 22 has been tuned to block the first RF QHTS
60 and the second RF QHTS 62.
[0058] As shown in FIGS. 2E and 2F, the first RF QHRS 56 has a
signal bandwidth 64 and the second RF QHRS 58 has a signal
bandwidth 66. Although the first RF QHRS 56 and the second RF QHRS
58 have approximately half the power spectral density (excluding
losses) of the RF receive input signal 14 shown in FIG. 2A, the
signal bandwidth 64 of the first RF QHRS 56 and the signal
bandwidth 66 of the second RF QHRS 58 are approximately the same
size and are located at approximately the same frequencies. In
FIGS. 2E and 2F, the signal bandwidth 64 of the first RF QHRS 56
and the signal bandwidth 66 of the second RF QHRS 58 are between
the frequencies f.sub.RBW1 and f.sub.RBW2. Both the signal
bandwidth 64 and the signal bandwidth 66 are approximately equal to
the signal bandwidth 40 (FIG. 2A) of the RF receive input signal
14. However, non-ideal circuit behavior may result in either slight
misalignments and/or slight size differences in the signal
bandwidth 64 and the signal bandwidth 66. The amount of error that
is permissible may depend on the particular application and
spectrum requirements. As mentioned above, the tuning circuit 24 is
configured to tune the frequency response 48 of the RF filter
circuit 22 so that the signal bandwidth 64 of the first RF QHRS 56
and the signal bandwidth 66 of the second RF QHRS 58 are each
within the passband 50. Consequently, the RF filter circuit 22
filters the first RF QHRS 56 and the second RF QHRS 58 to pass the
first RF QHRS 56 and the second RF QHRS 58 within the passband 50
to the second hybrid coupler 20.
[0059] As shown in FIGS. 2E and 2F, the first RF QHTS 60 has a
signal bandwidth 68, while the second RF QHTS 62 has a signal
bandwidth 70. Although the first RF QHTS 60 and the second RF QHTS
62 have approximately half the power spectral density of the RF
transmission input signal 26 (excluding losses), the signal
bandwidth 68 of the first RF QHTS 60 and the signal bandwidth 70 of
the second RF QHTS 62 are configured to be approximately the same
as the signal bandwidth 43 of the RF transmission input signal 26.
In the embodiments illustrated in FIGS. 2E and 2F, the signal
bandwidth 68 and the signal bandwidth 70 are both between the
frequencies f.sub.TBW1 and f.sub.TBW2. However, non-ideal circuit
behavior may result in slight misalignments or size differences in
the signal bandwidth 68 and the signal bandwidth 70. The amount of
error that is permissible may depend on the particular application
and spectrum requirements. The tuning circuit 24 is configured to
tune the frequency response 48 of the RF filter circuit 22 so that
the signal bandwidth 68 of the first RF QHTS 60 and the signal
bandwidth 70 of the second RF QHTS 62 are each within the stopband
52. In this manner, the RF filter circuit 22 blocks the first RF
QHTS 60 and the second RF QHTS 62 such that the first RF QHTS 60
and the second RF QHTS 62 are reflected back to the first hybrid
coupler 18.
[0060] Referring now to FIGS. 2 and 2G, FIG. 2G illustrates one
embodiment of the RF receive output signal 30 and one embodiment of
the RF transmission output signal 16. To provide the RF receive
output signal 30, the second hybrid coupler 20 combines the first
RF QHRS 56 (shown in FIG. 2E) and the second RF QHRS 58 (shown in
FIG. 2F) within the passband 50 (shown in FIGS. 2E and 2F) into the
RF receive output signal 30 (procedure 1016). As shown in FIG. 2G,
the RF receive output signal 30 operates within the RF receive band
36. Ideally, the RF receive output signal 30 has the same power
spectral density as the RF receive input signal 14. However, in
practice, the tunable RF duplexer 10 may not be lossless, and thus
the power spectral density of the RF receive output signal 30 may
be somewhat smaller than the power spectral density of the RF
receive input signal 14.
[0061] As shown in FIG. 2G, the RF receive output signal 30 has a
signal bandwidth 72 within the RF receive band 36. In this example,
the signal bandwidth 72 is the same as the signal bandwidth 40
(shown in FIG. 2A) of the RF receive input signal 14. Thus, the
signal bandwidth 72 is between the frequencies f.sub.RBW1 and
f.sub.RBW2. Furthermore, the RF receive output signal 30 operates
at the RF receive frequency f.sub.R, like the RF receive input
signal 14. However, this may not be exactly the case in all
circumstances. For example, the signal bandwidth 72 may be slightly
smaller, larger, or misaligned with the signal bandwidth 40 of the
RF receive input signal 14. There may also be a small frequency
displacement between the RF receive frequency of the RF receive
input signal 14 and the RF receive frequency f.sub.R of the RF
receive output signal 30. The amount of error permissible for these
parameters may depend on the particular application and/or spectrum
requirements. Furthermore, additional circuitry may be provided in
order to compensate for these errors.
[0062] Referring again to FIGS. 2 and 2G, FIG. 2G also illustrates
one embodiment of the RF transmission output signal 16. To provide
the RF transmission output signal 16, the first hybrid coupler 18
combines the first RF QHTS 60 (shown in FIG. 2E) and the second RF
QHTS 62 (shown in FIG. 2F) within the stopband 52 (shown in FIGS.
2E and 2F) into the RF transmission output signal 16 (procedure
1018). Ideally, the RF transmission output signal 16 has the same
power spectral density as the RF transmission input signal 26 shown
in FIG. 2A. However, the tunable RF duplexer 10 may not be
lossless, and thus, the power spectral density of the RF
transmission output signal 16 may be smaller. As shown in FIG. 2G,
the RF transmission output signal 16 has a signal bandwidth 74. The
signal bandwidth 74 may be the same as the signal bandwidth 43
(shown in FIG. 2A) of the RF transmission input signal 26. Thus, in
FIG. 2G, the signal bandwidth 74 of the RF transmission output
signal 16 is between the frequency f.sub.TBW1 and f.sub.TBW2.
However, this may not be the case. For example, the signal
bandwidth 74 may be smaller, larger, or misaligned with the signal
bandwidth 43. Also, the RF transmission output signal 16 shown in
FIG. 2G operates at the RF transmission frequency f.sub.T, like the
RF transmission input signal 26. This may or may not be the case.
For example, there may be a small displacement between the RF
transmission frequency f.sub.T of the RF transmission output signal
16 and the RF transmission frequency f.sub.T of the RF transmission
input signal 26. The amount of error that is permissible in these
parameters may depend on a particular application and/or spectrum
requirements.
[0063] FIG. 3A illustrates a tunable RF duplexer 10A along with a
receive signal flow of the tunable RF duplexer 10A. The tunable RF
duplexer 10A includes the first hybrid coupler 18, the second
hybrid coupler 20, an RF filter circuit 22A, and a tuning circuit
24A. As shown in FIG. 3A, the first hybrid coupler 18 has a first
port 76, a second port 78, a third port 80, and a fourth port 82,
while the second hybrid coupler 20 has a fifth port 84, a sixth
port 86, a seventh port 88, and an eighth port 90.
[0064] The antenna 12 intercepts the RF receive input signal 14 as
electromagnetic waves in free space. These electromagnetic waves
result in excitations within the antenna 12, thereby converting the
electromagnetic waves into the RF receive input signal 14. The
first hybrid coupler 18 is operable to receive the RF receive input
signal 14. In this particular embodiment, the first hybrid coupler
18 is coupled to receive the RF receive input signal 14 at the
first port 76 from the antenna 12. The first hybrid coupler 18 is
operable to split the RF receive input signal 14 into the first RF
QHRS 56 and the second RF QHRS 58. In this manner, the first RF
QHRS 56 and the second RF QHRS 58 have approximately the same power
ratio with respect to the RF receive input signal 14, but have a
quadrature phase difference of approximately 90 degrees or .pi./2
radians with respect to one another.
[0065] With regard to the first hybrid coupler 18 shown in FIG. 3A,
the first port 76 is phase-aligned with the third port 80, while
the first port 76 has a quadrature phase shift with respect to the
fourth port 82. Thus, the first RF QHRS 56 at the third port 80 is
approximately phase-aligned with the RF receive input signal 14 at
the first port 76, but there is a quadrature phase difference
between the RF receive input signal 14 at the first port 76 and the
second RF QHRS 58 at the fourth port 82.
[0066] Note that in alternative embodiments, this may or may not be
the case. For example, there may be a phase shift between the first
port 76 and the third port 80 (such as +45 degrees or +.pi./4
radians). The phase shift between the first port 76 and the fourth
port 82 may then be equal to this phase shift plus or minus 90
degrees (such as +135 degrees or +3.pi./4 radians, -45 degrees or
-.pi./4 radians). Accordingly, so long as the phase difference
between the first RF QHRS 56 and the second RF QHRS 58 is about 90
degrees or .pi./2 radians, phase alignment between the third port
80 and the first port 76, and between the fourth port 82 and the
first port 76, can vary.
[0067] The first RF QHRS 56 is output at the third port 80 to the
RF filter circuit 22A. Additionally, the second RF QHRS 58 is
output at the fourth port 82 to the RF filter circuit 22A. In this
embodiment, the RF filter circuit 22A has a first RF filter 92 (an
embodiment of the RF filter 23A shown in FIG. 1) and a second RF
filter 94 (an embodiment of the RF filter 23B shown in FIG. 1). The
first RF filter 92 is coupled to the third port 80 so as to receive
the first RF QHRS 56 from the first hybrid coupler 18. The second
RF filter 94 is coupled to the fourth port 82 so as to receive the
second RF QHRS 58 from the first hybrid coupler 18. The first RF
filter 92 and the second RF filter 94 each have a frequency
response. The frequency response of the RF filter circuit 22A is
thus determined in accordance with the combined effect of the
independent frequency responses provided by the first RF filter 92
and the second RF filter 94. However, in this embodiment, the first
RF filter 92 and the second RF filter 94 are identical to one
another. As such, the overall frequency response of the RF filter
circuit 22A is the same as the independent frequency responses
provided by the first RF filter 92 or the second RF filter 94.
Alternatively, in other embodiments, the first RF filter 92 and the
second RF filter 94 may be different and/or may be tuned
independently by the tuning circuit 24A. As such, the different
independent frequency responses from the first RF filter 92 and the
second RF filter 94 may combine to determine the overall frequency
response of the RF filter circuit 22A.
[0068] Referring again to FIG. 3A, the tuning circuit 24A is
configured to tune the frequency response of the RF filter circuit
22A so that the passband includes the RF receive band. The tuning
circuit 24A thus shifts the passband of the RF filter circuit 22A
to include the RF receive band. In this manner, the RF filter
circuit 22A is operable to pass the first RF QHRS 56 and the second
RF QHRS 58 to the second hybrid coupler 20. The manner of tuning
the frequency response may depend on the topology of the RF filter
circuit 22A. For example, the first RF filter 92 and the second RF
filter 94 shown in FIG. 3A may both be passive filters.
Accordingly, one or more reactive impedance components (inductive,
capacitive, or both) in each of the first and second RF filters 92,
94 may have a variable reactive impedance level. By varying these
variable reactive impedance levels, the poles and zeros of the
individual frequency responses provided by each of the first and
second RF filters 92, 94 are adjusted. This thereby shifts the
passband and/or the stopband of the RF filter circuit 22A. Ideally,
the first RF filter 92 and the second RF filter 94 in FIG. 3A each
operate as a short with respect to the RF receive band and as an
open circuit with respect to the RF transmission band.
[0069] The tuning circuit 24A illustrated in FIG. 3A generates a
receive tuning control output 96 and a transmission tuning control
output 98. The variable reactive impedance components in both the
first RF filter 92 and the second RF filter 94 are set in
accordance with one or more signal levels of the receive tuning
control output 96. In this manner, the stopband is shifted to
include the RF transmission band in accordance with one or more
signal levels of the transmission tuning control output 98.
Similarly, reactive impedance levels of variable reactive
components in the first RF filter 92 and the second RF filter 94
are set in accordance with one or more signal levels of the receive
tuning control output 96. The RF filter circuit 22A may also
include active RF filters, Surface Acoustic Wave (SAW) filters, or
any other type of RF filter or combination of RF filters that is
suitable to provide a desired frequency response. As such, the
tuning circuit 24A may employ various types of tuning topologies,
depending on the particular filtering topology being employed by
the RF filter circuit 22A.
[0070] By placing the passband in the RF receive band, the RF
filter circuit 22A passes the first RF QHRS 56 and the second RF
QHRS 58 to the second hybrid coupler 20. In this particular
embodiment, the first RF filter 92 passes the first RF QHRS 56 to
the second hybrid coupler 20, while the second RF filter 94 passes
the second RF QHRS 58 to the second hybrid coupler 20. As mentioned
above, the passband is set in the RF receive band.
[0071] Referring again to FIG. 3A, the second hybrid coupler 20
receives the first RF QHRS 56 from the first RF filter 92 at the
fifth port 84. The second RF QHRS 58 is received by the second
hybrid coupler 20 from the second RF filter 94 at the sixth port
86. As discussed above, the first RF QHRS 56 and the second RF QHRS
58 have a quadrature phase difference of about 90 degrees or .pi./2
radians. Thus, for example, if the first RF QHRS 56 has a phase of
zero degrees, the second RF QHRS 58 would have a phase of
approximately 90 degrees (or .pi./2 radians). From the fifth port
84 to the seventh port 88, the second hybrid coupler 20 provides no
phase shift. Alternatively, the second hybrid coupler 20 may be
configured to provide a phase shift from the fifth port 84 to the
seventh port 88 of .DELTA. (i.e., such as +45 degrees or .pi./4
radians).
[0072] The second hybrid coupler 20 shown in FIG. 3A is configured
to provide a quadrature phase shift from the sixth port 86 to the
seventh port 88. In this example, the phase shift is 90 degrees (or
.pi./2 radians), and thus the second RF QHRS 58 has a phase, as
seen from the seventh port 88, of 180 degrees (note that the second
RF QHRS 58 was received with a phase of 90 degrees in this example,
and thus is seen with a phase of 180 degrees with another phase
shift of 90 degrees). Alternatively, the phase shift from the sixth
port 86 to the seventh port 88 may be .DELTA..+-.90 degrees (or
.pi./2 radians). In any case, the phase difference between the
first RF QHRS 56 and the second RF QHRS 58 as seen from the seventh
port 88 is about 180 degrees (note that the first RF QHRS 56 was
received with a phase of zero (0) degrees and thus is seen with a
phase of zero (0) degrees at the seventh port 88). Accordingly, the
quadrature phase shift at the seventh port 88 from the sixth port
86 results in destructive interference between the first RF QHRS 56
and the second RF QHRS 58 at the seventh port 88. As a result, the
first RF QHRS 56 and the second RF QHRS 58 are substantially
cancelled at the seventh port 88. In this manner, the seventh port
88 is substantially isolated from receive signal flow.
[0073] The second hybrid coupler 20 is configured to output the RF
receive output signal 30 from the eighth port 90 in response to the
first RF QHRS 56 being received from the RF filter circuit 22A at
the fifth port 84 and the second RF QHRS 58 being received from the
RF filter circuit 22A at the sixth port 86. In this particular
embodiment, the second hybrid coupler 20 is configured to pass the
second RF QHRS 58 from the sixth port 86 to the eighth port 90. The
second hybrid coupler 20 provides no phase shift to the second RF
QHRS 58 from the sixth port 86 to the eighth port 90. The second RF
QHRS 58 is thus passed with a phase of 90 degrees to the eighth
port 90. Alternatively, the second hybrid coupler 20 may provide a
phase shift of .DELTA. (i.e., such as +45 degrees or .pi./4
radians) to the second RF QHRS 58 when passed from the sixth port
86 to the eighth port 90. The second hybrid coupler 20 is
configured to pass the first RF QHRS 56 from the fifth port 84 to
the eighth port 90. The second hybrid coupler 20 provides a
quadrature phase shift to the first RF QHRS 56 at the eighth port
90. In this embodiment, the quadrature phase shift is 90 degrees or
.pi./2 radians. Alternatively, if a phase shift of .DELTA. was
provided to the second RF QHRS 58 from the sixth port 86 to the
eighth port 90, the quadrature phase shift would be .DELTA..+-.90
degrees (or .pi./2 radians).
[0074] Accordingly, the first RF QHRS 56 is provided substantially
as a duplicate of the second RF QHRS 58 at the eighth port 90. This
is a result of the quadrature phase shift provided to the first RF
QHRS 56 when passed from the fifth port 84 to the eighth port 90
(now, at the eighth port 90, the first RF QHRS 56 is shifted to
have a phase of 90 degrees, just like the second RF QHRS 58).
Referring again to the example discussed previously, if the first
RF QHRS 56 has a phase of zero at the fifth port 84, then the first
RF QHRS 56 has a phase of 90 degrees at the eighth port 90. If the
phase of the second RF QHRS 58 at the sixth port 86 is 90 degrees,
then the phase of the second RF QHRS 58 is also 90 degrees at the
eighth port 90. Accordingly, the first RF QHRS 56 is substantially
a duplicate of the second RF QHRS 58 at the eighth port 90 because
the first RF QHRS 56 and the second RF QHRS 58 become phase-aligned
at the eighth port 90. As a result, the first RF QHRS 56 and the
second RF QHRS 58 constructively interfere at the eighth port 90 to
output the RF receive output signal 30 from the eighth port 90.
Note that since the first RF QHRS 56 and the second RF QHRS 58
substantially cancel at the seventh port 88 due to destructive
interference, very little or no power is transferred from the first
RF QHRS 56 and the second RF QHRS 58 to the seventh port 88.
Instead most, if not all, of the power in the first RF QHRS 56 and
the second RF QHRS 58 is transferred to the eighth port 90 and
provided in the RF receive output signal 30.
[0075] An impedance load 100 is coupled to the seventh port 88 of
the second hybrid coupler 20. The impedance load 100 may be a 50
Ohm load. Due to the phase-shifting provided by the first hybrid
coupler 18 and the second hybrid coupler 20, spurious emissions
from the second port 78 of the first hybrid coupler 18 would see a
very high (theoretically infinite) impedance level at the eighth
port 90 of the second hybrid coupler, but only the impedance load
100 at the seventh port 88. Thus, the spurious emissions are
aggregated to be an aggregated noise signal 102 at the seventh port
88. This aggregated noise signal 102 is dissipated by the impedance
load 100. Additionally, the eighth port 90 is isolated from the
seventh port 88. As such, the seventh port 88 is substantially
unresponsive to signals incident at the eighth port 90 and the
seventh port 88 is substantially unresponsive to signals incident
at the eighth port 90.
[0076] Additionally, an antenna impedance tuner 104 is coupled
between the antenna 12 and the first port 76. Since the RF
transmission output signal 16 is in the RF transmission band, the
impedance of the antenna 12 may result in a portion of the RF
transmission output signal 16 being reflected back to the first
port 76. This not only would degrade the RF transmission output
signal 16, but would also degrade the isolation between the receive
signal flow and the eighth port 90. The antenna impedance tuner 104
is tunable so as to reduce reflections from the antenna 12 to the
first port 76. More specifically, an impedance of the antenna 12
may be tuned so as to provide impedance matching between the first
port 76 and the antenna 12.
[0077] FIG. 3B illustrates the tunable RF duplexer 10A along with
the transmission signal flow. The RF filter circuit 32A may be
coupled to the power amplifier 28 to receive the RF transmission
input signal 26. The RF filter circuit 32A may be tunable so as to
define a stopband. The tuning circuit 24A may be configured to tune
the RF filter circuit 32A to provide the stopband within the RF
receive band. In particular, the RF filter circuit 32A is operable
to receive the transmission tuning control output 98 from the
tuning circuit 24A, which tunes the stopband accordingly. As a
result, the RF filter circuit 32A is operable to filter out
spurious emissions resulting from upstream RF circuitry, such as
the power amplifier 28, that are within the RF receive band.
[0078] The first hybrid coupler 18 is operable to receive the RF
transmission input signal 26 at the second port 78. The RF
transmission input signal 26 operates in the RF transmission band,
which is within the same RF communication band as the RF receive
band of the RF receive input signal 14 (see FIG. 2A). The first
hybrid coupler 18 is operable to split the RF transmission input
signal 26 into the first RF QHTS 60 and the second RF QHTS 62.
Since the first RF QHTS 60 and the second RF QHTS 62 are quadrature
hybrids, the first RF QHTS 60 and the second RF QHTS 62 are
approximately equal in power, but have a quadrature phase
difference of 90 degrees or .pi./2 radians. The first hybrid
coupler 18 is operable to output the first RF QHTS 60 from the
fourth port 82 and to output the second RF QHTS 62 from the third
port 80 in response to receiving the RF transmission input signal
26 at the second port 78.
[0079] In the embodiment illustrated in FIG. 3B, the first RF QHTS
60 is phase-aligned with the RF transmission input signal 26, while
the second RF QHTS 62 has a phase difference of about 90 degrees
with respect to the RF transmission input signal 26. It should be
noted that this may or may not be the case. For example, in
alternative embodiments, a phase shift of .DELTA. (i.e., +45
degrees or .pi./4 radians) may be provided between the second port
78 and the fourth port 82, and thus, a phase shift of .DELTA..+-.90
degrees (or .pi./2 radians) would be provided between the second
port 78 and the fourth port 82.
[0080] The RF filter circuit 22A is operable to reflect the first
RF QHTS 60 and the second RF QHTS 62. As discussed above, the
frequency response of the RF filter circuit 22A defines the
stopband and the RF filter circuit 22A is tunable so as to shift
the stopband. For example, the stopband may be a notch that is
shiftable. The tuning circuit 24A is configured to tune the
frequency response of the RF filter circuit 22A so that the signal
bandwidth of the first RF QHTS 60 and the signal bandwidth of the
second RF QHTS 62 are each within the stopband. For instance, the
tuning circuit 24A may be configured to place the notch within the
RF transmission band so that the notch is centered at the RF
transmission signal frequency. In this embodiment, the tuning
circuit 24A generates the transmission tuning control output 98.
Variable reactive impedance components in both the first RF filter
92 and the second RF filter 94 are responsive to the one or more
signal levels of the transmission tuning control output 98 so as to
adjust the variable impedance levels based on the signal level(s)
of the transmission tuning control output 98. As a result, the
notch defined by the individual frequency response of the first RF
filter 92 is shifted to include the signal bandwidth of the second
RF QHTS 62. Also, the notch defined by the individual frequency
response of the second RF filter 94 is shifted to include the
signal bandwidth of the first RF QHTS 60. In other words, the
notches defined by the individual frequency responses of the first
RF filter 92 and the second RF filter 94 are placed in the RF
transmission band.
[0081] Since the tuning circuit 24A has tuned the frequency
response of the RF filter circuit 22A so that the stopband includes
the RF transmission signal band, the RF filter circuit 22A blocks
the first RF QHTS 60 and the second RF QHTS 62. Accordingly, the
second hybrid coupler 20 is substantially isolated from the
transmission signal flow. The RF filter circuit 22A then reflects
the first RF QHTS 60 and the second RF QHTS 62 back to the first
hybrid coupler 18. In the embodiment illustrated in FIG. 3B, the
second RF filter 94 reflects the first RF QHTS 60 back to the first
hybrid coupler 18 at the fourth port 82. The first RF filter 92
reflects the second RF QHTS 62 back to the first hybrid coupler 18
at the third port 80.
[0082] The first hybrid coupler 18 is configured to combine the
first RF QHTS 60 and the second RF QHTS 62 into the RF transmission
output signal 16. To combine the first RF QHTS 60 and the second RF
QHTS 62 into the RF transmission output signal 16, the first hybrid
coupler 18 is configured to pass the second RF QHTS 62 from the
fourth port 82 to the first port 76. Additionally, the first hybrid
coupler 18 is configured to pass the first RF QHTS 60 from the
fourth port 82 to the first port 76. However, the first hybrid
coupler 18 provides a quadrature phase shift to the first RF QHTS
60 from the fourth port 82 to the first port 76. Thus, the first RF
QHTS 60 is provided substantially as a duplicate of the second RF
QHTS 62 at the first port 76. For example, if the phase of the
second RF QHTS 62 is 90 degrees at the third port 80, the second RF
QHTS 62 has a phase of 90 degrees at the first port 76.
Additionally, the phase of the first RF QHTS 60 at the third port
80 is approximately zero degrees. However, due to the quadrature
phase shift between the fourth port 82 and the first port 76, the
first RF QHTS 60 has a phase of about 90 degrees at the first port
76. Accordingly, the first RF QHTS 60 and the second RF QHTS 62
constructively interfere at the first port 76 to output the RF
transmission output signal 16 from the first port 76.
[0083] Also, note that the first hybrid coupler 18 is configured
such that the quadrature phase shift at the second port 78 results
in destructive interference between the first RF QHTS 60 and the
second RF QHTS 62. Referring again to the previous example
provided, at the second port 78, the first RF QHTS 60 appears to
have a phase of zero degrees, but the second RF QHTS 62 appears to
have a phase of 180 degrees. As a result, the first RF QHTS 60 and
the second RF QHTS 62 are substantially cancelled at the second
port 78. Consequently, most, if not all, of the power of the first
RF QHTS 60 and the second RF QHTS 62 is transferred to the first
port 76 and provided in the RF transmission output signal 16. The
first hybrid coupler 18 is thus configured to output the RF
transmission output signal 16 from the first port 76 in response to
the first RF QHTS 60 being reflected back by the RF filter circuit
22A to the fourth port 82 and the second RF QHTS 62 being reflected
back by the RF filter circuit 22A to the third port 80.
[0084] Note that spurious emissions from the first RF QHTS 60 and
the second RF QHTS 62 that are not reflected by the RF filter
circuit 22A, such as spurious noise emissions outside the stopband,
may be passed toward the second hybrid coupler 20. In this example,
the spurious emissions would destructively interfere at the eighth
port 90 and constructively interfere at the seventh port 88.
Accordingly, these spurious emissions become part of the aggregated
noise signal 102 and are dissipated by the impedance load 100.
Therefore, the tunable RF duplexer 10A significantly reduces noise
interference resulting at the second port 78 of the first hybrid
coupler 18 from degrading the RF receive output signal 30 at the
eighth port 90.
[0085] As shown in FIGS. 3A and 3B, the tunable RF duplexer 10A
allows the receive signal flow and the transmission signal flow to
be simultaneous. More specifically, the first port 76 of the first
hybrid coupler 18 is configured to simultaneously receive the RF
receive input signal 14 and output the RF transmission output
signal 16 to and from the antenna 12. As a result, the RF
transmission output signal 16 is output from the first port 76
while the RF receive input signal 14 is being received at the first
port 76. The tunable RF duplexer 10A can provide this functionality
because the second port 78 is substantially isolated from the
eighth port 90.
[0086] Note that the first RF filter 92 in the RF filter circuit
22A is coupled in series between the third port 80 of the first
hybrid coupler 18 and the fifth port 84 of the second hybrid
coupler 20. Furthermore, the second RF filter 94 in the RF filter
circuit 22A is coupled in series between the fourth port 82 of the
first hybrid coupler 18 and the sixth port 86 of the second hybrid
coupler 20. As noted above, the stopband of the RF filter circuit
22A, and thus the stopband of each of the first and second RF
filters 92, 94, should reflect the first RF QHTS 60 and the second
RF QHTS 62. As a result, an impedance of the second RF filter 94
should appear very high within the RF transmission band as seen
from the fourth port 82, and an impedance of the first RF filter 92
should appear very high within the RF transmission band as seen
from the third port 80. Ideally, the impedance of the second RF
filter 94 as seen from the fourth port 82 and the impedance of the
first RF filter 92 as seen from the third port 80 should be
infinite. In practice, these impedances should simply be high
enough to meet RF communication band specifications.
[0087] Additionally, the passband of the RF filter circuit 22A, and
thus the passband of each of the first and second RF filters 92,
94, should pass the first RF QHRS 56 and the second RF QHRS 58. The
first and second RF filters 92, 94 should therefore appear
transparent in the RF receive band. Since the first and second RF
filters 92, 94 are coupled in series, the input/output impedances
of each of the first and second RF filters 92, 94 would ideally be
the same as the characteristic impedance of the intra-hybrid
connection lines. In practice, the input/output impedances of each
of the first and second RF filters 92, 94 may simply be provided
sufficiently near the characteristic impedance of the intra-hybrid
connection lines such that RF communication band specifications are
met. Nevertheless, tuning by the tuning circuit 24A can be
difficult to implement when the first and second RF filters 92, 94
are coupled in series, as shown in FIGS. 3A and 3B.
[0088] Referring now to FIG. 4, FIG. 4 illustrates one embodiment
of a frequency response 48A provided by the RF filter circuit 22A
shown in FIGS. 3A and 3B. The frequency response 48A defines a
passband 50A and a stopband 52A. The RF filter circuit 22A
described in FIGS. 3A and 3B is tunable so that the RF
communication band (referred to generically as element 34 and
specifically as elements 34A-34E) can be switched to be any one of
a plurality of different RF communication bands 34A-34E. The
different RF communication bands 34A-34E may each define different
RF receive band(s) and different RF transmission band(s) within
each of the RF communication bands 34A-34E. Accordingly, the RF
transmission input signal 26 (shown in FIGS. 3A-3B) and the RF
receive input signal 14 (shown in FIGS. 3A-3B) may be in the
respective RF receive band and RF transmission band of any of the
different RF communication bands 34A-34E. Accordingly, the first RF
QHRS 56, the second RF QHRS 58, and the RF receive output signal 30
would also operate within the RF receive band of the RF receive
input signal 14. Similarly, the first RF QHTS 60, the second RF
QHTS 62, and the RF transmission output signal 16 would operate in
the respective RF transmission band of the RF transmission input
signal 26.
[0089] When the RF communication band 34 is switched to be a
different one of the plurality of RF communication bands 34A-34E,
the tuning circuit 24A is operable to tune the frequency response
48A to the particular RF communication band 34A-34E. Since the RF
communication band 34 has been switched, the first RF QHRS 56 and
the second RF QHRS 58 are provided in the new RF communication band
34A-34E. In particular, the first RF QHRS 56 and the second RF QHRS
58 operate within the RF receive band of the new RF communication
band 34A-34E. Also, since the RF communication band 34 has been
switched to the new RF communication band 34A-34E, the first RF
QHTS 60 and the second RF QHTS 62 are provided within the new RF
communication band 34A-34E. In particular, the first RF QHTS 60 and
the second RF QHTS 62 operate within the RF transmission band of
the new RF communication band 34A-34E. The tuning circuit 24A tunes
the passband 50A so as to pass the first RF QHRS 56 and the second
RF QHRS 58 in response to the RF communication band 34 being
switched to the new RF communication band 34A-34E. More
particularly, the passband 50A is provided so as to include the RF
receive band of the selected RF communication band 34A-34E.
Similarly, the tuning circuit 24A shifts the stopband 52A to
reflect the first RF QHTS 60 and the second RF QHTS 62 in response
to the RF communication band 34 being switched to the new RF
communication band 34A-34E. More particularly, the stopband 52A is
shifted to include the RF transmission band of the selected RF
communication band 34A-34E.
[0090] FIG. 5 illustrates another embodiment of a tunable RF
duplexer 10B. The tunable RF duplexer 10B is similar to the tunable
RF duplexer 10A shown in FIGS. 3A and 3B. The tunable RF duplexer
10B has a first hybrid coupler 18' and a second hybrid coupler 20',
an RF filter circuit 22B, and a tuning circuit 24B. The RF filter
circuit 22B is another embodiment of the RF filter circuit 22 in
FIG. 1. As explained in further detail below, the first hybrid
coupler 18' and the second hybrid coupler 20' operate in the same
manner as the first hybrid coupler 18 and second hybrid coupler 20
described above in FIGS. 3A and 3B, except in this embodiment the
first hybrid coupler 18' and the second hybrid coupler 20' are
tunable. Also, like the RF filter circuit 22A shown in FIGS. 3A and
3B, the RF filter circuit 22B has a frequency response that defines
a stopband and a passband and is tunable so as to shift the
passband and the stopband. However, a first RF filter 106 has an
individual frequency response that defines a passband and a
stopband. Unlike the RF filter circuit 22A shown in FIGS. 3A and
3B, the RF filter circuit 22B in FIG. 5 has the first RF filter 106
and a second RF filter 108 coupled in shunt. More specifically, the
first RF filter 106 is coupled in shunt between the third port 80
and the fifth port 84, while the second RF filter 108 is coupled in
shunt between the fourth port 82 and the sixth port 86.
[0091] The tuning circuit 24B illustrated in FIG. 5 is configured
to tune the RF filter circuit 22B so as to shift the passband to
within the RF receive band of the RF receive input signal 14 and
the stopband to within the RF transmission input signal 26. More
specifically, the first RF filter 106 has an individual frequency
response that defines a passband and a stopband. The second RF
filter 108 also has an individual frequency response that defines a
passband and a stopband. As such, the different independent
frequency responses from the first RF filter 106 and the second RF
filter 108 may combine to determine the overall frequency response
of the RF filter circuit 22B. Alternatively, in other embodiments,
the first RF filter 106 and the second RF filter 108 may be
different, and/or may be tuned independently by the tuning circuit
24B. As such, the different independent frequency responses from
the first RF filter 106 and the second RF filter 108 may combine to
determine the overall frequency response of the RF filter circuit
22B.
[0092] The tuning circuit 24B shown in FIG. 5 is configured to
generate a receive tuning control output 110, hybrid control
outputs (referred to generically as element 111 and specifically as
elements 111A and 111B), and a transmission tuning control output
112. The variable reactive impedance components of both the first
RF filter 106 and the second RF filter 108 are set in accordance
with one or more signal levels of the receive tuning control output
110. In this manner, the passbands of both the first RF filter 106
and the second RF filter 108 are shifted within the RF receive band
of the RF receive input signal 14. The second hybrid coupler 20' is
operable to output the RF receive output signal 30 at the eighth
port 90. Additionally, reactive impedance levels of variable
reactive components in both the first RF filter 106 and the second
RF filter 108 are set in accordance with a signal level of the
transmission tuning control output 112. In this manner, the
stopbands of both the first RF filter 106 and the second RF filter
108 are shifted within the RF transmission band of the RF
transmission input signal 26 at the second port 78. The first
hybrid coupler 18' is configured to output the RF transmission
output signal 16 at the first port 76. As such, the tunable RF
duplexer 10B is configured to simultaneously receive the RF receive
input signal 14 from the antenna 12 and output the RF transmission
output signal 16 to the antenna 12. The tuning of the first hybrid
coupler 18' by the first hybrid control output 111A and the tuning
of the second hybrid coupler 20' by the second hybrid control
output 111B is described in further detail below.
[0093] FIG. 6A illustrates the tunable RF duplexer 10B along with a
receive signal flow. The antenna 12 intercepts the RF receive input
signal 14 as electromagnetic waves in free space. These
electromagnetic waves result in excitations within the antenna 12,
thereby converting the electromagnetic waves into the RF receive
input signal 14. The first hybrid coupler 18' is operable to
receive the RF receive input signal 14 at the first port 76.
[0094] The first hybrid coupler 18' is operable to split the RF
receive input signal 14 into the first RF QHRS 56 and the second RF
QHRS 58. In this manner, the first RF QHRS 56 and the second RF
QHRS 58 have approximately the same power ratio with respect to the
RF receive input signal 14, but have a quadrature phase difference
of approximately 90 degrees or .pi./2 radians with respect to one
another. The first RF QHRS 56 is output at the third port 80 to the
RF filter circuit 22B. Additionally, the second RF QHRS 58 is
output at the fourth port 82 to the RF filter circuit 22B.
[0095] The tuning circuit 24B is configured to tune the frequency
response so that a signal bandwidth of the first RF QHRS 56 and a
signal bandwidth of the second RF QHRS 58 are each within the
passband of the RF filter circuit 22B. In this embodiment, the
tuning circuit 24B is configured to tune the passband of the first
RF filter 106 within the signal bandwidth of the first RF QHRS 56
and to tune the passband of the second RF filter 108 within the
signal bandwidth of the second RF QHRS 58. To provide each of the
passbands, the first RF filter 106 and the second RF filter 108
each appear approximately as open circuits. Since the first RF
filter 106 is coupled in shunt, the first RF filter 106 appears
approximately transparent within the passband of the first RF
filter 106. Similarly, since the second RF filter 108 is coupled in
shunt, the second RF filter 108 appears approximately transparent
within the passband of second RF filter 108. Unlike the series
coupled first and second RF filters 92, 94 shown in FIGS. 3A and
3B, the input/output impedances of the first RF filter 106 and the
second RF filter 108 in FIG. 6A do not have to approximate the
characteristic impedance of the intra-hybrid connection lines in
order to appear transparent. This may make it easier to implement
the tuning circuit 24B. Also, since the first RF filter 106 and the
second RF filter 108 are coupled in shunt, the first RF filter 106
and the second RF filter 108 can provide paths for neutralizing
parasitic loading effects within the RF receive band using reactive
compensation.
[0096] By placing the passband in the RF receive band, the RF
filter circuit 22B passes the first RF QHRS 56 and the second RF
QHRS 58 to the second hybrid coupler 20'. In this particular
embodiment, the first RF filter 106 passes the first RF QHRS 56 to
the second hybrid coupler 20', while the second RF filter 108
passes the second RF QHRS 58 to the second hybrid coupler 20'. More
specifically, the first RF QHRS 56 is received at the fifth port 84
of the second hybrid coupler 20', and the second RF QHRS 58 is
received at the sixth port 86 of the second hybrid coupler 20'.
[0097] As described above with respect to FIG. 3A, the second
hybrid coupler 20' shown in FIG. 3A is configured to provide a
quadrature phase shift from the sixth port 86 to the seventh port
88. In this example, the phase shift is 90 degrees (or .pi./2
radians), and thus the second RF QHRS 58 has a phase, as seen from
the seventh port 88, of 180 degrees (note that the second RF QHRS
58 was received with a phase of 90 degrees in this example, and
thus is seen with a phase of 180 degrees with another phase shift
of 90 degrees). No phase shift is provided from the fifth port 84
to the eighth port 90. Thus, the phase difference between the first
RF QHRS 56 and the second RF QHRS 58 as seen from the seventh port
88 is about 180 degrees (note that the first RF QHRS 56 was
received with a phase of zero (0) degrees and thus is seen with a
phase of zero (0) degrees at the seventh port 88). Accordingly, the
quadrature phase shift at the seventh port 88 from the sixth port
86 results in destructive interference between the first RF QHRS 56
and the second RF QHRS 58 at the seventh port 88. As a result, the
first RF QHRS 56 and the second RF QHRS 58 are substantially
cancelled at the seventh port 88. In this manner, the seventh port
88 is substantially isolated from receive signal flow.
[0098] The second hybrid coupler 20' is configured to output the RF
receive output signal 30 from the eighth port 90 in response to the
first RF QHRS 56 being received from the RF filter circuit 22B at
the fifth port 84 and the second RF QHRS 58 being received from the
RF filter circuit 22B at the sixth port 86. In this particular
embodiment, the second hybrid coupler 20' is configured to pass the
second RF QHRS 58 from the sixth port 86 to the eighth port 90. The
second hybrid coupler 20' provides no phase shift to the second RF
QHRS 58 from the sixth port 86 to the eighth port 90. Since no
phase shift is provided to the second RF QHRS 58 from the sixth
port 86 to the eighth port 90, the second RF QHRS 58 is thus passed
with a phase of 90 degrees (or .pi./2 radians) to the eighth port
90. The second hybrid coupler 20' is configured to provide a
quadrature phase shift to the first RF QHRS 56 at the eighth port
90. Thus, since the quadrature phase shift is provided to the first
RF QHRS 56 from the fifth port 84 to the eighth port 90, the second
RF QHRS 58 is passed with a phase of 90 degrees (or .pi./2 radians)
to the eighth port 90.
[0099] Accordingly, the first RF QHRS 56 is provided substantially
as a duplicate of the second RF QHRS 58 at the eighth port 90. As a
result, the first RF QHRS 56 and the second RF QHRS 58
constructively interfere at the eighth port 90 to output the RF
receive output signal 30 from the eighth port 90. Note that since
the first RF QHRS 56 and the second RF QHRS 58 substantially cancel
at the seventh port 88 due to destructive interference, very little
or no power is transferred from the first RF QHRS 56 and the second
RF QHRS 58 to the seventh port 88. Instead most, if not all, of the
power in the first RF QHRS 56 and the second RF QHRS 58 is
transferred to the eighth port 90 and provided in the RF receive
output signal 30.
[0100] The impedance load 100 is coupled to the seventh port 88 of
the second hybrid coupler 20'. The impedance load 100 may be a 50
Ohm load. Due to the phase-shifting provided by the first hybrid
coupler 18' and the second hybrid coupler 20', spurious emissions
from the second port 78 of the first hybrid coupler 18 would see a
very high (theoretically infinite) impedance level at the eighth
port 90 of the second hybrid coupler, but only the impedance load
100 at the seventh port 88. Thus, the spurious emissions are
aggregated to be the aggregated noise signal 102 at the seventh
port 88. The aggregated noise signal 102 is dissipated by the
impedance load 100. Additionally, the eighth port 90 is isolated
from the seventh port 88. As such, the seventh port 88 is
substantially unresponsive to signals incident at the eighth port
90 and the eighth port 90 is substantially unresponsive to signals
incident at the seventh port 88.
[0101] FIG. 6B illustrates the tunable RF duplexer 10B along with
the transmission signal flow. The first hybrid coupler 18' is
operable to receive the RF transmission input signal 26 at the
second port 78. The RF transmission input signal 26 operates in the
RF transmission band, which is within the same RF communication
band as the RF receive band of the RF receive input signal 14 (see
FIG. 2A). The first hybrid coupler 18' is configured to split the
RF transmission input signal 26 into the first RF QHTS 60 and the
second RF QHTS 62. Since the first RF QHTS 60 and the second RF
QHTS 62 are quadrature hybrids, the first RF QHTS 60 and the second
RF QHTS 62 are approximately equal in power, but have a quadrature
phase difference of 90 degrees or .pi./2 radians. The first hybrid
coupler 18' is operable to output the first RF QHTS 60 from the
fourth port 82 and to output the second RF QHTS 62 from the third
port 80 in response to receiving the RF transmission input signal
26 at the second port 78.
[0102] The RF filter circuit 22B is tunable so as to reflect the
first RF QHTS 60 and the second RF QHTS 62 back to the first hybrid
coupler 18'. The frequency response of the RF filter circuit 22B
defines a stopband and the RF filter circuit 22B is tunable so as
to shift the stopband. For example, the stopband may be a notch
that is shiftable. The tuning circuit 24B is configured to tune the
frequency response of the RF filter circuit 22B so that the signal
bandwidth of the first RF QHTS 60 and the signal bandwidth of the
second RF QHTS 62 are each within the stopband of the RF filter
circuit 22B. In this embodiment, the tuning circuit 24B is
configured to tune a stopband of the second RF filter 108 within
the signal bandwidth of the first RF QHTS 60 and to tune a stopband
of the first RF filter 106 within the signal bandwidth of the
second RF QHTS 62. To provide each of the stopbands, the first RF
filter 106 and the second RF filter 108 each appear approximately
as short circuits within the RF transmission band.
[0103] In this embodiment, the frequency response of the RF filter
circuit 22B defines the stopband of the RF filter circuit 22B as a
notch. The tuning circuit 24B may be configured to place the notch
within the RF transmission band so that the notch is centered at
the RF transmission signal frequency. More specifically, the
frequency response of the first RF filter 106 defines its stopband
as a notch. Similarly, the frequency response of the second RF
filter 108 is a notch. The tuning circuit 24B is configured to
generate the transmission tuning control output 112 such that
variable reactive impedance components in both the first RF filter
106 and the second RF filter 108 are responsive to one or more
signal levels of the transmission tuning control output 112 and
adjust the variable impedance levels based on the one or more
signal levels of the transmission tuning control output 112. As a
result, the notch defined by the individual frequency response of
the first RF filter 106 is shifted to include the signal bandwidth
of the second RF QHTS 62. Also, the notch defined by the individual
frequency response of the second RF filter 108 is shifted to
include the signal bandwidth of the first RF QHTS 60. In other
words, the notches defined by the individual frequency responses of
the first RF filter 106 and the second RF filter 108 are placed
within the RF transmission band.
[0104] Since the first RF filter 106 is coupled in shunt and
operates approximately as a short in the RF transmission band, the
first RF filter 106 reflects the second RF QHTS 62 back to the
third port 80 of the first hybrid coupler 18'. Also, since the
second RF filter 108 is coupled in shunt and operates approximately
as a short in the RF transmission band, the second RF filter 108
reflects the first RF QHTS 60 back to the fourth port 82 of the
first hybrid coupler 18'. Accordingly, the second hybrid coupler
20' is substantially isolated from the transmission signal flow.
The first hybrid coupler 18' is configured to combine the first RF
QHTS 60 and the second RF QHTS 62 into the RF transmission output
signal 16. To combine the first RF QHTS 60 and the second RF QHTS
62 into the RF transmission output signal 16, the first hybrid
coupler 18' is configured to pass the second RF QHTS 62 from the
third port 80 to the first port 76. Additionally, the first hybrid
coupler 18' is configured to pass the first RF QHTS 60 from the
fourth port 82 to the first port 76. However, the first hybrid
coupler 18' provides a quadrature phase shift to the first RF QHTS
60 from the fourth port 82 to the first port 76. Thus, the first RF
QHTS 60 is provided substantially as a duplicate of the second RF
QHTS 62 at the first port 76. For example, if the phase of the
second RF QHTS 62 is 90 degrees at the third port 80, the second RF
QHTS 62 has a phase of 90 degrees at the first port 76.
Additionally, the phase of the first RF QHTS 60 at the fourth port
82 is approximately zero (0) degrees. However, due to the
quadrature phase shift between the fourth port 82 and the first
port 76, the first RF QHTS 60 has a phase of about 90 degrees at
the first port 76. Accordingly, the first RF QHTS 60 and the second
RF QHTS 62 constructively interfere at the first port 76 to output
the RF transmission output signal 16 from the first port 76.
[0105] Also, note that the first hybrid coupler 18' is configured
such that the quadrature phase shift at the second port 78 results
in destructive interference between the first RF QHTS 60 and the
second RF QHTS 62. Referring again to the previous example
provided, at the second port 78, the first RF QHTS 60 appears to
have a phase of zero degrees, but the second RF QHTS 62 appears to
have a phase of 180 degrees. As a result, the first RF QHTS 60 and
the second RF QHTS 62 are substantially cancelled at the second
port 78. Consequently, most, if not all, of the power of the first
RF QHTS 60 and the second RF QHTS 62 is transferred to the first
port 76 and provided in the RF transmission output signal 16. The
first hybrid coupler 18' is thus configured to output the RF
transmission output signal 16 from the first port 76 in response to
the first RF QHTS 60 being reflected back by the RF filter circuit
22B to the fourth port 82 and the second RF QHTS 62 being reflected
back by the RF filter circuit 22B to the third port 80.
[0106] Note that spurious emissions from the first RF QHTS 60 and
the second RF QHTS 62 may not be reflected by the RF filter circuit
22B. Instead, spurious noise emissions outside the stopband, may be
passed toward the second hybrid coupler 20'. In this example, the
spurious emissions would destructively interfere at the eighth port
90 and constructively interfere at the seventh port 88.
Accordingly, these spurious emissions become part of the aggregated
noise signal 102 and are dissipated by the impedance load 100.
Therefore, the tunable RF duplexer 10B significantly reduces noise
interference from the second port 78 of the first hybrid coupler
18' (see FIG. 3A) at the eighth port 90.
[0107] As shown in FIGS. 6A and 6B, the tunable RF duplexer 10B
allows the receive signal flow and the transmission signal flow to
be simultaneous. More specifically, the first port 76 of the first
hybrid coupler 18' is configured to simultaneously receive the RF
receive input signal 14 and output the RF transmission output
signal 16 to and from the antenna 12. As a result, the RF
transmission output signal 16 is output from the first port 76
while the RF receive input signal 14 is being simultaneously
received at the first port 76. The tunable RF duplexer 10B can
provide this functionality because the second port 78 is
substantially isolated from the eighth port 90.
[0108] Referring now to FIG. 7, FIG. 7 illustrates one embodiment
of a frequency response 48B provided by the RF filter circuit 22B
shown in FIGS. 6A and 6B. The frequency response 48B defines a
passband 50B and a stopband 52B. The RF filter circuit 22B
described in FIGS. 6A and 6B is tunable so that the RF
communication band (referred to generically as element 34, and
specifically as elements 34A-34E) can be switched to be any one of
the plurality of different RF communication bands 34A-34E. The
different RF communication bands 34A-34E may each define different
RF receive band(s) and different RF transmission band(s) within
each of the RF communication bands 34A-34E. Accordingly, the RF
transmission input signal 26 (shown in FIGS. 6A-6B) and the RF
receive input signal 14 (shown in FIGS. 6A-6B) may be in the
respective RF receive band and RF transmission band of any of the
different RF communication bands 34A-34E. Accordingly, the first RF
QHRS 56, the second RF QHRS 58, and the RF receive output signal 30
would also operate within the RF receive band of the RF receive
input signal 14. Similarly, the first RF QHTS 60, the second RF
QHTS 62, and the RF transmission output signal 16 would operate in
the respective RF transmission band of the RF transmission input
signal 26.
[0109] When the RF communication band 34 is switched to be a
different one of the plurality of RF communication bands 34A-34E,
the tuning circuit 24B is operable to tune the frequency response
48B to the particular RF communication band 34A-34E. Since the RF
communication band 34 has been switched, the first RF QHRS 56 and
the second RF QHRS 58 are provided in the new RF communication band
34A-34E. In particular, the first RF QHRS 56 and the second RF QHRS
58 operate within the RF receive band of the new RF communication
band 34A-34E. Also, since the RF communication band 34 has been
switched to the new RF communication band 34A-34E, the first RF
QHTS 60 and the second RF QHTS 62 are provided within the new RF
communication band 34A-34E. In particular, the first RF QHTS 60 and
the second RF QHTS 62 operate within the RF transmission band of
the new RF communication band 34A-34E. The tuning circuit 24B tunes
the passband 50B so as to pass the first RF QHRS 56 and the second
RF QHRS 58 in response to the RF communication band 34 being
switched to the new RF communication band 34A-34E. More
particularly, the passband 50B is provided so as to include the RF
receive band of the selected RF communication band 34A-34E.
Similarly, the tuning circuit 24B shifts the stopband 52B to
reflect the first RF QHTS 60 and the second RF QHTS 62 in response
to the RF communication band 34 being switched to the new RF
communication band 34A-34E. As such, the stopband 52B is shifted to
include the RF transmission band of the selected RF communication
band 34A-34E.
[0110] Referring to FIGS. 6A, 6B, and 8A, FIG. 8A illustrates one
embodiment of a tunable hybrid coupler 114. In practice, the
tunable RF duplexer 10B shown in FIGS. 6A and 6B may not be able to
provide infinite transmission/receive isolation. For example,
impedance mismatches between the first hybrid coupler 18' and the
second hybrid coupler 20' may result in small reflections and leaks
that degrade transmission/receive isolation. To help reduce and/or
eliminate these reflections and leaks, the first hybrid coupler 18'
and the second hybrid coupler 20' are tunable. As mentioned above,
the first hybrid coupler 18' and the second hybrid coupler 20' in
FIGS. 6A and 6B may each be tunable. Accordingly, in one exemplary
embodiment of the tunable RF duplexer 10B, the first hybrid coupler
18' and the second hybrid coupler 20' are each provided as the
tunable hybrid coupler 114 of FIG. 8A.
[0111] The tunable hybrid coupler 114 shown in FIG. 8A is a
lumped-element hybrid coupler. However, the tunable hybrid coupler
114 may be implemented using any suitable hybrid coupler topology.
In alternative embodiments, the tunable hybrid coupler 114 may be a
rat-race hybrid coupler, transmission line coupler, Wilkinson
hybrid coupler, stripline hybrid coupler, microstrip hybrid
coupler, ferrite core hybrid coupler, amalgamations of different
types of hybrid couplers, and/or the like. The tunable hybrid
coupler 114 has a first port 116, a second port 118, a third port
120, and a fourth port 122. With regard to the first hybrid coupler
18' shown in FIGS. 6A-6B, the first port 116 of the tunable hybrid
coupler 114 corresponds to the first port 76 of the first hybrid
coupler 18', the second port 118 of the tunable hybrid coupler 114
corresponds to the second port 78 of the first hybrid coupler 18',
the third port 120 of the tunable hybrid coupler 114 corresponds to
the third port 80 of the first hybrid coupler 18', and the fourth
port 122 of the tunable hybrid coupler 114 corresponds to the
fourth port 82 of the first hybrid coupler 18'. With regard to the
second hybrid coupler 20' shown in FIGS. 6A-6B, the first port 116
of the tunable hybrid coupler 114 corresponds to the fifth port 84
of the second hybrid coupler 20', the second port 118 of the
tunable hybrid coupler 114 corresponds to the sixth port 86 of the
second hybrid coupler 20', the third port 120 of the tunable hybrid
coupler 114 corresponds to the seventh port 88 of the second hybrid
coupler 20', and the fourth port 122 of the tunable hybrid coupler
114 corresponds to the eighth port 90 of the second hybrid coupler
20'.
[0112] The tunable hybrid coupler 114 shown in FIG. 8A includes a
first inductive element 124 and a second inductive element 126. The
first inductive element 124 is connected in series between the
fourth port 122 and the second port 118. The second inductive
element is connected in series between the third port 120 and the
first port 116. In this embodiment, the first inductive element 124
and the second inductive element 126 are inductively coupled and
have a coupling coefficient k that is equal to approximately one
(1). As such, the first inductive element 124 is operable to
generate a magnetic flux in response to a current propagating on
the first inductive element 124. The magnetic flux generated by the
first inductive element 124 also flows within the second inductive
element 126. The magnetic flux thus induces an electromotive force
on the second inductive element 126 so as to generate a current
that propagates on the second inductive element 126. However, a
quadrature phase shift of 90 degrees or .pi./2 radians is provided
from the first inductive element 124 to the second inductive
element 126. The current that propagates on the second inductive
element 126 has a phase of 90 degrees or .pi./2 radians with
respect to the current that propagates through the first inductive
element 124. Since the coupling coefficient k between the first
inductive element 124 and the second inductive element 126 is one
(1), the currents propagating on the first inductive element 124
and the second inductive element 126 have approximately the same
magnitude. In other words, half of the power (ignoring parasitic
and non-ideal circuit behavior) is transferred through the magnetic
flux from the first inductive element 124 and the second inductive
element 126.
[0113] Similarly, the second inductive element 126 is operable to
generate a magnetic flux in response to a current propagating on
the second inductive element 126. The magnetic flux generated by
the second inductive element 126 also flows within the first
inductive element 124. The magnetic flux thus induces an
electromotive force on the first inductive element 124 so as to
generate a current that propagates on the first inductive element
124. However, a quadrature phase shift of 90 degrees or .pi./2
radians is provided from the second inductive element 126 to the
first inductive element 124. The current that propagates on the
first inductive element 124 has a phase of 90 degrees or .pi./2
radians with respect to the current that propagates through the
second inductive element 126. Since the coupling coefficient k
between the second inductive element 126 and the first inductive
element 124 is one (1), the currents propagating on the second
inductive element 126 and the first inductive element 124 have
approximately the same magnitude. In other words, half of the power
(ignoring parasitic and non-ideal circuit behavior) is transferred
through the magnetic flux from the second inductive element 126 to
the first inductive element 124. In this embodiment, the first
inductive element 124 has a first inductance and the second
inductive element 126 has a second inductance, wherein the first
inductance and the second inductance are the same.
[0114] Accordingly, the tunable hybrid coupler 114 is configured to
split an RF signal received at one of the ports 116, 118, 120, 122
into a pair of RF quadrature hybrid signals (QHS). One of the RF
QHS generated from the splitting of the RF signal propagates
through the inductive element 124,126 in series with the port 116,
118, 120, 122 that received the RF signal. The tunable hybrid
coupler 114 is configured to output this RF QHS from the other port
120, 122, 116, 118 in series with the inductive element 124, 126.
In this embodiment, the RF QHS output from the other port 120, 122,
116, 118 in series with the inductive element 124, 126 is
phase-aligned with the RF signal. However, in alternative
embodiments, a phase shift of .DELTA. (i.e., such as +45 degrees or
+.pi./4 radians) may be provided from the port 116, 118, 120, 122
that receives the RF signal and the other port 120, 122, 116, 118
in series with the inductive element 124, 126.
[0115] The other RF QHS generated from the splitting of the RF
signal propagates through the other inductive element 126,124 that
is inductively coupled with the inductive element 124,126. Each RF
QHS has half the spectral power density of the RF signal received
at the port 116, 118, 120, 122. The other RF QHS propagates in the
same direction as the RF signal. Thus, the tunable hybrid coupler
114 is configured to output the other RF QHS propagating on the
other inductive element 126,124 at the port 122, 120, 118, 116. In
this embodiment, the other RF QHS output from the port 122, 120,
118, 116 has a phase of +90 degrees or +.pi./2 radians with respect
to the RF signal. However, in alternative embodiments, a phase
shift of .DELTA..+-.90 degrees (such as +135 degrees or +3.pi./4
radians, -45 degrees or -.pi./4 radians) may be provided from the
port 116, 118, 120, 122 that receives the RF signal and the port
122, 120, 118, 116 that outputs the other RF QHS. Furthermore, note
that that the port 118, 116, 122, 120 is isolated from the port
116, 118, 120, 122 that received the RF signal. As mentioned above,
the first hybrid coupler 18' and the second hybrid coupler 20' of
FIGS. 6A and 6B may each be implemented as the tunable hybrid
coupler 114 shown in FIG. 8A. In this manner, the tunable RF
duplexer 10B can simultaneously receive the RF receive input signal
14 and the RF transmission input signal 26, generate the first RF
QHRS 56, the second RF QHRS 58, the first RF QHTS 60, and the
second RF QHTS 62, and output the RF receive output signal 30 and
the RF transmission output signal 16, as described above with
respect to FIGS. 6A and 6B.
[0116] Referring to FIG. 8A, the tunable hybrid coupler 114
includes a variable capacitive element 128 and a variable
capacitive element 130. The variable capacitive element 128 is
connected between the first port 116 and the second port 118. The
variable capacitive element 128 is operable to provide a first
variable capacitance. As a result, a first variable capacitive
impedance is presented by the variable capacitive element 128
between the first port 116 and the second port 118. In addition,
the variable capacitive element 130 is coupled between the third
port 120 and the fourth port 122. The variable capacitive element
130 is operable to provide a second variable capacitance. As a
result, a second variable capacitive impedance is presented by the
variable capacitive element 130 between the third port 120 and the
fourth port 122.
[0117] Accordingly, the first inductive element 124, the second
inductive element 126, the variable capacitive element 128, and the
variable capacitive element 130 form an impedance matching network
for a 4-port system. The impedance matching network provides
impedance transformations so as to increase impedance matching
between input and output impedances at the first port 116, the
second port 118, the third port 120, and the fourth port 122. The
term "input impedance" refers to an internal impedance at the
respective port 116, 118, 120, 122 toward the tunable hybrid
coupler 114. "Output impedance" refers to an external impedance at
the respective port 116, 118, 120, 122 out of the tunable hybrid
coupler 114. The impedance matching network also provides an
impedance transformation so as to increase impedance matching
between an impedance from the first port 116 to the second port 118
and an impedance from the third port 120 to the fourth port
122.
[0118] In this embodiment, the impedance matching network provides
an impedance transformation that increases impedance matching
between an input impedance and an output impedance at the first
port 116. Additionally, the impedance matching network provides an
impedance transformation that increases impedance matching between
an input impedance and an output impedance at the second port 118.
The impedance matching network also provides an impedance
transformation that increases impedance matching between an input
impedance and an output impedance at the third port 120. Finally,
the impedance matching network provides an impedance transformation
that increases impedance matching between an input impedance and an
output impedance at the fourth port 122.
[0119] As shown in FIG. 8A, the tunable hybrid coupler 114 also
includes a variable capacitive element 132 and a variable
capacitive element 134. The variable capacitive element 132 is
connected between the first port 116 and the third port 120 in
parallel with the first inductive element 124. The variable
capacitive element 132 is operable to provide a third variable
capacitance. As a result, a third variable capacitive impedance is
presented by the variable capacitive element 132 between the first
port 116 and the third port 120 in parallel with the first
inductive element 124. In addition, the variable capacitive element
134 is coupled between the second port 118 and the fourth port 122
in parallel with the inductive element 126. The variable capacitive
element 134 is operable to provide a fourth variable capacitance.
As a result, a fourth variable capacitive impedance is presented by
the variable capacitive element 134 between the second port 118 and
the fourth port 122 in parallel with the inductive element 126. The
variable capacitive element 132 and the variable capacitive element
134 allow for more accurate tuning of the impedance
transformations. Additionally, the variable capacitive element 132
in parallel with the first inductive element 124 can be used to
define a notch. Similarly, the variable capacitive element 134 in
parallel with the second inductive element 136 can also be used to
define a notch.
[0120] Accordingly, the variable capacitive element 128, the
variable capacitive element 130, the variable capacitive element
132, and the variable capacitive element 134 allow the tunable
hybrid coupler 114 to be tuned. In this manner, the tunable hybrid
coupler 114 is operable to provide impedance transformations to
increase impedance matching of the input and output impedances at
the first port 116, the second port 118, the third port 120, and
the fourth port 122 within different RF communication bands.
Ideally, the tunable hybrid coupler 114 perfectly matches the input
impedances and the output impedances at each of the ports 116,
118,120, 122. However, in practice, there may be some mismatches
between input and output impedances despite the impedance
transformations. An acceptable amount of mismatch may depend on the
particular application for the tunable hybrid coupler 114 along
with RF communication band specifications. For example, the tunable
hybrid coupler 114 shown in FIG. 8A is sufficiently broadband such
that the impedance transformations increase matching of the input
and output impedances both within the transmission frequency band
and the receive frequency band of a selected RF communication band.
However, for any selected capacitance value of the variable
capacitances, the tunable hybrid coupler 114 may not be capable of
providing perfect matching within both the transmission frequency
band and the receive frequency band and/or the transmission
frequency and the receive frequency simultaneously. Therefore, in
some circumstances, the variable capacitances may be selected at an
interpolated point that does not provide perfect matching within or
at either the transmission frequency band/transmission frequency or
the receive frequency band/receive frequency.
[0121] The tunable hybrid coupler 114 is configured to received the
hybrid control output 111 (in FIGS. 6A-6B, the first hybrid coupler
18' is operable to receive the first hybrid control output 111A and
the second hybrid coupler 20' is operable to receive the second
hybrid control output 111B). The hybrid control output 111 includes
one or more hybrid control signals 111-1, 111-2, 111-3, and 111-4.
Each of the variable capacitive elements 128, 130, 132, 134 is
configured to set its respective variable capacitance in accordance
with a signal level of a corresponding one of the hybrid control
signals 111-1, 111-2, 111-3, and 111-4. For example, the variable
capacitive element 128 is configured to set the first variable
capacitance in accordance with a signal level of the hybrid control
signal 111-1. Additionally, the variable capacitive element 130 is
configured to set the second variable capacitance in accordance
with a signal level of the hybrid control signal 111-2.
Furthermore, the variable capacitive element 132 is configured to
set the third variable capacitance in accordance with a signal
level of the hybrid control signal 111-3. Finally, the variable
capacitive element 134 is configured to set the third variable
capacitance in accordance with a signal level of the hybrid control
signal 111-4. Thus, the first variable capacitance, the second
variable capacitance, the third variable capacitance, and the
fourth variable capacitance are each configured to be adjusted in
accordance with the respective signal level of the corresponding
one of the respective hybrid control signals 111-1, 111-2, 111-3,
and 111-4. In this manner, the tunable hybrid coupler 114 can be
tuned to increase impedance matching between input and output
impedances at the ports 116, 118,120, 122 within the different RF
communication bands.
[0122] FIG. 8B illustrates one embodiment of the tunable hybrid
coupler 114 formed on a semiconductor substrate 136. The
semiconductor substrate 136 has a substrate body 138 formed from a
wafer and/or doped layers of a suitable semiconductor material. For
example, the semiconductor material may be Silicon (Si), Silicon
Germanium (SiGe), Gallium Arsenide (GaAs), Indium Phosphorus (InP),
and/or the like. Typical dopants that may be utilized to dope the
semiconductor layers are Gallium (Ga), Arsenic (As), Silicon (Si),
Tellurium (Te), Zinc (Zn), Sulfur (S), Boron (B), Phosphorus (P),
Aluminum Gallium Arsenide (AlGaAs), Indium Gallium Arsenide
(InGaAs), and/or the like. Furthermore, metallic layers, insulating
layers, and the like may be formed on one or more surfaces or
within the substrate body 138 to provide terminals, traces, coils,
connections, passive impedance elements, active semiconductor
components, and/or the like. Also, any type of suitable
semiconductor technology may be used to provide the topology of the
semiconductor substrate 136. For example, the semiconductor
technology may be Complementary Metal-On-Oxide Semiconductor
technology (CMOS), BiComplementary Metal-On-Oxide Semiconductor
technology (BiCMOS), Silicon-On-Insulator technology (SOI), and/or
the like. In this embodiment, the semiconductor technology of the
semiconductor substrate 136 is SOI, and thus the semiconductor
material of the substrate body 138 is Si. Additionally, the
substrate body 138 has a surface 140. The surface 140 thus defines
a direction 142 normal to the surface 140. Terms in this disclosure
referring to directional words such as "over" or "top" and "under"
or "beneath" are made with respect to the direction 142 defined by
the surface 140 of the substrate body 138. It should be noted that
the first hybrid coupler 18', the second hybrid coupler 20', the
first RF filter 106, and the second RF filter 108 shown in FIGS. 6A
and 6B may be formed with the same semiconductor substrate 136, or
one or more of these components may be formed on one or more
separate semiconductor substrates.
[0123] As shown in FIG. 8B, the first port 116, the second port
118, the third port 120, and the fourth port 122 are each formed as
a terminal on the surface 140 of the substrate body 138. In this
manner, RF signals may be input and/or output from the tunable
hybrid coupler 114. The first inductive element 124 is formed as a
spiral coil on the surface 140. The first inductive element 124 and
the first port 116, the second port 118, the third port 120, and
the fourth port 122 may be formed from a metallic layer on the
surface 140 that has been etched to provide the first inductive
element 124 and the first port 116, the second port 118, the third
port 120, and the fourth port 122. At a center of the spiral coil,
the first inductive element 124 shown in FIG. 8B defines a central
axis 144 approximately parallel to the direction 142 and thus
normal to the surface 140. The first inductive element 124 is wound
about the central axis 144 to form turns that have increasing
circumferences the more outwardly the turns are from the central
axis 144. Additionally, the second inductive element 126 is formed
as a spiral coil within the substrate body 138. The second
inductive element 126 may be formed from a metallic layer within
the substrate body 138. The metallic layer may be formed on a layer
beneath the surface 140 and etched to provide the second inductive
element 126. At a center of the spiral coil, the second inductive
element 126 shown in FIG. 8B defines a central axis 146
approximately parallel to the direction 142 and thus normal to the
surface 140. The second inductive element 126 is wound about the
central axis 146 to form turns that have increasing circumferences
the more outwardly the turns are from the central axis 146. The
first inductive element 124 and the second inductive element 126
are inductively coupled so that the magnetic flux of each one of
the inductive elements 124, 126 induces a current in the other one
of the inductive elements 126, 124.
[0124] FIG. 8B also illustrates the variable capacitive elements
128, 130, 132, and 134, which are formed as variable
metal-insulator-metal capacitors in the semiconductor substrate
136. However, with the arrangement shown in FIG. 8B, the first
inductive element 124 and the second inductive element 126 are
configured so that there is a parasitic capacitance between the
first inductive element 124 and the second inductive element 126.
In this embodiment, the parasitic capacitance between the first
inductive element 124 and the second inductive element 126 is
significantly greater than a highest capacitive value of the
variable capacitances provided by the variable capacitive elements
128, 130, 132, and 134. As such, the largest and greatest
capacitive impedance is from this parasitic capacitance between the
inductive elements 126, 124. Also, the parasitic capacitance sets a
minimum capacitance between the first inductive element 124 and the
second inductive element 126. While the variable capacitance of the
variable capacitive element 128 can be used to adjust a capacitive
impedance as seen between the first port 116 and the second port
118 and the variable capacitance of the variable capacitive element
130 can be used to adjust a capacitive impedance as seen between
the third port 120 and the fourth port 122, the primary capacitive
impedance between the first port 116 and the second port 118 and
between the third port 120 and the fourth port 122 is from the
parasitic capacitance between the first inductive element 124 and
the second inductive element 126.
[0125] As such, the parasitic capacitance between the first
inductive element 124 and the second inductive element 126 sets a
minimum capacitance of the tunable hybrid coupler 114. Note that in
this embodiment, there is a displacement along the surface 140 from
the central axis 144 of the first inductive element 124 to the
central axis 146 of the second inductive element 126. Since the
first inductive element 124 and the second inductive element 126
are approximately parallel, this displacement sets the parasitic
capacitance and the minimum capacitance of the tunable hybrid
coupler 114. Accordingly, when manufacturing the tunable hybrid
coupler 114, this displacement may be selected to set the parasitic
capacitance in accordance with a frequency range of the different
RF communication bands for a particular design application. During
operation, adjustments can be made to the variable capacitances of
the variable capacitive elements 128, 130, 132, and 134 so as to
tune the tunable hybrid coupler 114 to a selected one of the
different RF communication bands.
[0126] FIG. 9A illustrates another embodiment of a tunable hybrid
coupler 114'. Like the tunable hybrid coupler 114 shown in FIG. 8A,
the tunable hybrid coupler 114' also has the first port 116, the
second port 118, the third port 120, and the fourth port 122.
Similarly, with regard to the first hybrid coupler 18' shown in
FIGS. 6A-6B, the first port 116 of the tunable hybrid coupler 114'
corresponds to the first port 76 of the first hybrid coupler 18',
the second port 118 of the tunable hybrid coupler 114' corresponds
to the second port 78 of the first hybrid coupler 18', the third
port 120 of the tunable hybrid coupler 114' corresponds to the
third port 80 of the first hybrid coupler 18', and the fourth port
122 of the tunable hybrid coupler 114' corresponds to the fourth
port 82 of the first hybrid coupler 18'. With regard to the second
hybrid coupler 20' shown in FIGS. 6A-6B, the first port 116 of the
tunable hybrid coupler 114' corresponds to the fifth port 84 of the
second hybrid coupler 20', the second port 118 of the tunable
hybrid coupler 114' corresponds to the sixth port 86 of the second
hybrid coupler 20', the third port 120 of the tunable hybrid
coupler 114' corresponds to the seventh port 88 of the second
hybrid coupler 20', and the fourth port 122 of the tunable hybrid
coupler 114' corresponds to the eighth port 90 of the second hybrid
coupler 20'.
[0127] Also like the tunable hybrid coupler 114 shown in FIG. 8A,
the tunable hybrid coupler 114' includes the first inductive
element 124 connected in series between the fourth port 122 and the
second port 118 and includes the second inductive element 126
connected in series between the third port 120 and the first port
116. The first inductive element 124 and the second inductive
element 126 are inductively coupled and have the coupling
coefficient k that is equal to approximately one (1).
[0128] Referring to FIG. 9A, the tunable hybrid coupler 114'
includes a variable capacitive element 128', a variable capacitive
element 130', a variable capacitive element 132', a variable
capacitive element 134', a variable capacitive element 148, and a
variable capacitive element 150. The variable capacitive element
128' is connected between the first port 116 and the second port
118 so as to provide a first variable capacitance between the first
port 116 and the second port 118.
[0129] As with the tunable hybrid coupler 114 illustrated in FIG.
8A, the first inductive element 124, the second inductive element
126, the variable capacitive element 128', and the variable
capacitive element 130' shown in FIG. 9A form an impedance matching
network for a 4-port system. The impedance matching network
provides impedance transformations so as to increase impedance
matching between input and output impedances at the first port 116,
the second port 118, the third port 120, and the fourth port 122.
Accordingly, the impedance matching network provides an impedance
transformation that increases impedance matching between an input
impedance and an output impedance at the first port 116.
Additionally, the impedance matching network provides an impedance
transformation that increases impedance matching between an input
impedance and an output impedance at the second port 118. The
impedance matching network also provides an impedance
transformation that increases impedance matching between an input
impedance and an output impedance at the third port 120. Finally,
the impedance matching network provides an impedance transformation
that increases impedance matching between an input impedance and an
output impedance at the fourth port 122.
[0130] As shown in FIG. 9A, the tunable hybrid coupler 114' also
includes the variable capacitive element 132' and the variable
capacitive element 134'. The variable capacitive element 132' is
connected between the first port 116 and the third port 120 in
parallel with the first inductive element 124. The variable
capacitive element 132' is operable to provide a third variable
capacitance. As a result, a third variable capacitive impedance is
presented by the variable capacitive element 132' between the first
port 116 and the third port 120 in parallel with the first
inductive element 124. In addition, the variable capacitive element
134' is coupled between the second port 118 and the fourth port 122
in parallel with the second inductive element 126. The variable
capacitive element 134' is operable to provide a fourth variable
capacitance. As a result, a fourth variable capacitive impedance is
presented by the variable capacitive element 134' between the
second port 118 and the fourth port 122 in parallel with the second
inductive element 126. The variable capacitive element 132' and the
variable capacitive element 134' allow for more accurate tuning of
the impedance transformations. Additionally, the variable
capacitive element 132' in parallel with the first inductive
element 124 can be used to define a notch. Similarly, the variable
capacitive element 134' in parallel with the second inductive
element 126 can be also used to define a notch.
[0131] However, in order to have strong inductive coupling between
the first inductive element 124 and the second inductive element
126, the first inductive element 124 and the second inductive
element 126 may have relatively large inductances for any given
minimum capacitance. The large inductances of the first inductive
element 124 and the second inductive element 126 could restrict a
frequency range for tuning the notches. In order to expand the
frequency range for the notches, the tunable hybrid coupler 114'
also includes the variable capacitive element 148 and the variable
capacitive element 150. The variable capacitive element 148 is
connected in parallel with a portion 152 of the first inductive
element 124. More specifically, the variable capacitive element 148
of FIG. 9A is connected from the first port 116 to an intermediary
node 154 of the first inductive element 124. The variable
capacitive element 148 is operable to provide a fifth variable
capacitance. As such, unlike the variable capacitive element 132',
the variable capacitive element 148 does not have to resonate with
the entire first inductive element 124 to create a notch. Rather,
the variable capacitive element 148 is configured to create the
notch by resonating with only the portion 152 of the first
inductive element 124. Since the portion 152 of the first inductive
element 124 has a smaller inductance than the entire first
inductive element 124, the notch created by the portion 152 of the
first inductive element 124 and the variable capacitive element 148
can be tuned to a greater frequency range than the frequency range
of the notch created by the variable capacitive element 132' and
the entire first inductive element 124.
[0132] Similarly, the variable capacitive element 150 is connected
in parallel with a portion 156 of the second inductive element 126.
More specifically, the variable capacitive element 150 of FIG. 9A
is connected from the second port 118 to an intermediary node 158
of the second inductive element 126. The variable capacitive
element 150 is operable to provide a sixth variable capacitance. As
such, unlike the variable capacitive element 134', the variable
capacitive element 150 does not have to resonate with the entire
second inductive element 126 to create a notch. Rather, the
variable capacitive element 150 is configured to create the notch
by resonating with only the portion 156 of the second inductive
element 126. Since the portion 156 of the second inductive element
126 has a smaller inductance than the entire second inductive
element 126, the notch created by the portion 156 of the second
inductive element 126 and the variable capacitive element 150 can
be tuned to a greater frequency range than the frequency range of
the notch created by the variable capacitive element 134' and the
entire second inductive element 126.
[0133] The tunable hybrid coupler 114' is configured to receive the
hybrid control output 111 (in FIGS. 6A-6B, the first hybrid coupler
18' is operable to receive the first hybrid control output 111A and
the second hybrid coupler 20' is operable to receive the second
hybrid control output 111B). However, in FIG. 9A, each of the
variable capacitive elements 128', 130', 132', 134', 148, and 150
is a programmable capacitor array (PCA). As such, each one of the
variable capacitive elements 128', 130', 132', 134', 148, and 150
includes a group of selectable capacitive components. These
selectable capacitive components in each of the variable capacitive
elements 128', 130', 132', 134', 148, and 150 can all have the same
fixed capacitances, or they may have different fixed capacitances.
To set the variable capacitance of each of the variable capacitive
elements 128', 130', 132', 134', 148, and 150, a particular
combination of the selectable capacitive components from a total
set of permissible combinations is selected in each of the variable
capacitive elements 128', 130', 132', 134', 148, and 150. Since the
selectable capacitive components each have fixed capacitances, the
variable capacitance of each of the variable capacitive elements
128', 130', 132', 134', 148, and 150 varies in a discrete manner
depending on the particular combination of the selectable
capacitive components that has been selected.
[0134] The hybrid control output 111 thus includes hybrid word
outputs 111-1', 111-2', 111-3', 111-4', 111-5', 111-6' for the
variable capacitive elements 128', 130', 132', 134', 148, and 150.
Each one of the hybrid word outputs 111-1', 111-2', 111-3', 111-4',
111-5', 111-6' may include one or more bit signals so that each one
of the hybrid word outputs 111-1', 111-2', 111-3', 111-4', 111-5',
111-6' represents a decoded word. The decoded word indicates the
particular combination of selectable capacitive components that are
to be selected in a corresponding one of the variable capacitive
elements 128', 130', 132', 134', 148, and 150. Thus, the decoded
word represents a particular discrete capacitance value for the
variable capacitance of the corresponding one of the variable
capacitive elements 128', 130', 132', 134', 148, and 150. Each of
the variable capacitive elements 128', 130', 132', 134', 148, and
150 is configured to set the variable capacitance in accordance
with a corresponding one of the hybrid word outputs 111-1', 111-2',
111-3', 111-4', 111-5', 111-6'.
[0135] For example, the variable capacitive element 128' is
configured to set the first variable capacitance in accordance to a
decoded word represented by the hybrid word output 111-1'. The
decoded word represents a particular combination of the selectable
capacitive components in the variable capacitive element 128'. The
variable capacitive element 128' is configured to select the
particular combination of the selectable capacitive components in
the variable capacitive element 128' in response to the hybrid word
output 111-1'. The variable capacitive element 130' is configured
to set the second variable capacitance in accordance to a decoded
word represented by the hybrid word output 111-2'. The decoded word
represents a particular combination of the selectable capacitive
components in the variable capacitive element 130'. The variable
capacitive element 130' is configured to select the particular
combination of the selectable capacitive components in the variable
capacitive element 130' in response to the hybrid word output
111-2'. The variable capacitive element 132' is configured to set
the third variable capacitance in accordance to a decoded word
represented by the hybrid word output 111-3'. The decoded word
represents a particular combination of the selectable capacitive
components in the variable capacitive element 132'. The variable
capacitive element 132' is configured to select the particular
combination of the selectable capacitive components in the variable
capacitive element 132' in response to the hybrid word output
111-3'. The variable capacitive element 134' is configured to set
the fourth variable capacitance in accordance to a decoded word
represented by the hybrid word output 111-4'. The decoded word
represents a particular combination of the selectable capacitive
components in the variable capacitive element 134'. The variable
capacitive element 134' is configured to select the particular
combination of the selectable capacitive components in the variable
capacitive element 134' in response to the hybrid word output
111-4'. The variable capacitive element 148 is configured to set
the fifth variable capacitance in accordance to a decoded word
represented by the hybrid word output 111-5'. The decoded word
represents a particular combination of the selectable capacitive
components in the variable capacitive element 148. The variable
capacitive element 148 is configured to select the particular
combination of the selectable capacitive components in the variable
capacitive element 148 in response to the hybrid word output
111-5'. The variable capacitive element 150 is configured to set
the sixth variable capacitance in accordance to a decoded word
represented by the hybrid word output 111-6'. The decoded word
represents a particular combination of the selectable capacitive
components in the variable capacitive element 150. The variable
capacitive element 150 is configured to select the particular
combination of the selectable capacitive components in the variable
capacitive element 150 in response to the hybrid word output
111-6'.
[0136] Thus, the first variable capacitance, the second variable
capacitance, the third variable capacitance, the fourth variable
capacitance, the fifth variable capacitance, and the sixth variable
capacitance are each configured to be adjusted in accordance with
the respective decoded word represented by the corresponding one of
the respective hybrid word outputs 111-1', 111-2', 111-3', 111-4',
111-5', 111-6'. In this manner, the tunable hybrid coupler 114' can
be tuned to increase impedance matching between input and output
impedances at the ports 116, 118,120, 122 within the different RF
communication bands.
[0137] FIG. 9B illustrates one embodiment of the tunable hybrid
coupler 114' formed on the semiconductor substrate 136. The first
port 116, the second port 118, the third port 120, the fourth port
122, the first inductive element 124, and the second inductive
element 126 are each formed in the same manner described above with
respect to the tunable hybrid coupler 114 shown in FIG. 8B.
However, unlike the tunable hybrid coupler 114 illustrated in FIG.
8B, each of the variable capacitive elements 128', 130', 132', and
134' in the tunable hybrid coupler 114' illustrated in FIG. 9B is
formed as a PCA in the semiconductor substrate 136. Additionally,
the tunable hybrid coupler 114' has the variable capacitive
elements 148, 150, each of which is also formed as a PCA in the
semiconductor substrate 136. The variable capacitive element 148 is
connected in parallel with the portion 152 of the first inductive
element 124. More specifically, the variable capacitive element 148
of FIG. 9B is connected from the first port 116 to the intermediary
node 154 of the first inductive element 124. Additionally, the
variable capacitive element 150 is connected in parallel with the
portion 156 of the second inductive element 126. More specifically,
the variable capacitive element 150 of FIG. 9A is connected from
the second port 118 to the intermediary node 158 of the second
inductive element 126. During operation, adjustments can be made to
the variable capacitances of the variable capacitive elements 128',
130', 132', 134', 148, 150 so as to tune the tunable hybrid coupler
114' to a selected one of the different RF communication bands.
[0138] FIGS. 10A-10E illustrate embodiments of RF filters 160, 162,
164, 166, 168, respectively. Each of the RF filters 160, 162, 164,
166, 168, is a shunt coupled RF filter. Accordingly, the first RF
filter 106 in the RF filter circuit 22B of FIGS. 6A and 6B can be
provided as any one of the RF filters 160, 162, 164, 166, 168,
shown in FIGS. 10A-10E. Similarly, the second RF filter 108 in the
RF filter circuit 22B of FIGS. 6A and 6B can be provided as any one
of the RF filters 160, 162, 164, 166, 168 shown in FIGS.
10A-10E.
[0139] Referring now to FIG. 10A, as the first RF filter 106 (see
FIG. 6A), the RF filter 160 is tunable to pass the first RF QHRS 56
(see FIG. 6A) to the second hybrid coupler 20' (see FIG. 6A), or,
as the second RF filter 108 (see FIG. 6A), the RF filter 160 is
tunable to pass the second RF QHRS 58 (see FIG. 6A) to the second
hybrid coupler 20' (see FIG. 6A). Also, as the second RF filter 108
(see FIG. 6B) the RF filter 160 is tunable to reflect the first RF
QHTS 60 (see FIG. 6B) back to the first hybrid coupler 18' (see
FIG. 6B), or, as the first RF filter 106 (see FIG. 6B), the RF
filter 160 is tunable to reflect the second RF QHTS 62 (see FIG.
6B) back to the first hybrid coupler 18' (see FIG. 6B). The RF
filter 160 includes a series LC resonator 170 and a variable
capacitive element 172 that are coupled in shunt between the first
hybrid coupler 18' and the second hybrid coupler 20'. The series LC
resonator 170 is thus connected in parallel with respect to the
variable capacitive element 172. The variable capacitive element
172 is operable to provide a variable capacitance. Thus, in this
embodiment, the variable capacitive element 172 is coupled to
present a variable capacitive impedance from a line 173 to ground.
The series LC resonator 170 includes an inductive element 174 and a
variable capacitive element 176 coupled in series with respect to
one another. The variable capacitive element 176 also has a
variable capacitance. The series LC resonator 170 is therefore
tunable by adjusting the variable capacitance of the variable
capacitive element 176. Thus, in this embodiment, the series LC
resonator 170 is coupled to present a variable reactive impedance
from the line 173 to ground.
[0140] The RF filter 160 has a frequency response that defines a
stopband (i.e., a notch). The series LC resonator 170 operates
approximately as a short circuit at a series resonant frequency of
the series LC resonator 170. Accordingly, the stopband of the RF
filter 160 is transposed, shifting the series resonant frequency,
which is done in this embodiment by adjusting the variable
capacitance of the variable capacitive element 176. To do this, the
variable capacitance of the variable capacitive element 176 is set
in response to the transmission tuning control output 112. The
transmission tuning control output 112 either represents a decoded
word or has a signal level that indicates the variable capacitance
value for setting the variable capacitance of the variable
capacitive element 176. In this manner, the series resonant
frequency is set at approximately the transmission frequency of the
RF transmission input signal 26 (see FIGS. 6A-6B), and the stopband
is shifted within the RF transmission band of the RF transmission
input signal 26 (see FIGS. 6A-6B).
[0141] The variable capacitive element 172 and the series LC
resonator 170 form a parallel LC resonator. The RF filter 160 thus
operates approximately as an open circuit at a parallel resonant
frequency of the parallel LC resonator. The frequency response of
the RF filter 160 thus also defines a passband. The parallel
resonant frequency is equal to approximately the series resonant
frequency plus a frequency offset. The frequency offset is
determined in accordance to the variable capacitance of the
variable capacitive element 172. Accordingly, the frequency offset
of the RF filter 160 from the series resonant frequency can be
transposed by adjusting the variable capacitance of the variable
capacitive element 176. To do this, the variable capacitance of the
variable capacitive element 176 is set in response to the receive
control output 110. The receive control output 110 either
represents a decoded word or has a signal level that indicates the
variable capacitance value for setting the variable capacitance of
the variable capacitive element 172. In this manner, the parallel
resonant frequency is set at approximately the receive frequency of
the RF receive input signal 14 (see FIGS. 6A-6B), and the passband
is shifted within the RF receive band of the RF receive input
signal 14 (see FIGS. 6A-6B). The RF filter 160 demonstrates good
performance when operating in 3G and 4G RF communication bands.
However, RF communication bands with smaller duplex offsets between
the RF transmission band and the RF communication band, such as
Long Term Evolution (LTE) RF communication bands, require a higher
quality factor performance.
[0142] FIG. 10B illustrates an embodiment of the RF filter 162. As
the first RF filter 106 (see FIG. 6A), the RF filter 162 is tunable
to pass the first RF QHRS 56 (see FIG. 6A) to the second hybrid
coupler 20' (see FIG. 6A), or, as the second RF filter 108 (see
FIG. 6A), the RF filter 162 is tunable to pass the second RF QHRS
58 (see FIG. 6A) to the second hybrid coupler 20' (see FIG. 6A).
Also, as the second RF filter 108 (see FIG. 6B), the RF filter 162
is tunable to reflect the first RF QHTS 60 (see FIG. 6B) back to
the first hybrid coupler 18' (see FIG. 6B), or, as the first RF
filter 106 (see FIG. 6B), the RF filter 162 is tunable to reflect
the second RF QHTS 62 (see FIG. 6B) back to the first hybrid
coupler 18' (see FIG. 6B). In this embodiment, the RF filter 162
has a plurality of SAW resonators (referred to generically as
element 178, and specifically as elements 178A-178F). The SAW
resonators 178 are formed on a piezo-electric substrate 180. These
SAW resonators 178 are selectable by a set of single-pole
multiple-throw switches (referred to generically as element 182,
and specifically as elements 182A and 182B). Alternatively, the RF
filter 162 (and the RF filters 164, 166, and 168) may only include
either the single-pole multiple-throw switch 182A (and not the
single-pole multiple-throw switch 182B) or the single-pole
multiple-throw switch 182B (and not the single-pole multiple-throw
switch 182A). In some embodiments, providing only the single-pole
multiple-throw switch 182A (and not the single-pole multiple-throw
switch 182B) or the single-pole multiple-throw switch 182B (and not
the single-pole multiple-throw switch 182A) has provided for a
better quality factor in comparison to using both of the
single-pole multiple-throw switches 182A, 182B in series.
[0143] Each of the SAW resonators 178 in FIG. 10B corresponds to a
different RF communication band. Essentially, each of the SAW
resonators 178 is configured to present an inductance in series
with a first capacitance and a second capacitance in parallel with
the inductance in series with the first capacitance. Each of the
SAW resonators 178 thus operates approximately as a short circuit
at a series resonant frequency of the inductance in series with the
first capacitance. Additionally, each of the SAW resonators 178
thus operates approximately as a open circuit at a parallel
resonant frequency of the second capacitance in parallel with the
inductance in series with the first capacitance. The inductance,
the first capacitance, and the second capacitance of each of the
SAW resonators 178 have different values. As such, a stopband and a
passband defined by a frequency response of the RF filter 162 are
tuned discretely by selecting a different one of the SAW resonators
178. The RF filter 162 shown in FIG. 10B has SAW resonators 178 for
six different RF communication bands. Optionally, each of the SAW
resonators 178 is connected in series with an inductive element
(referred to generically as elements 184, and specifically as
elements 184A-184F). Each of the inductive elements 184 has a
different inductance.
[0144] The SAW resonator 178A is selectable to set the stopband of
the RF filter 162 within a first RF transmission band of a first RF
communication band and to set the passband within a first RF
receive band of the first RF communication band. The inductance of
the inductive element 184A provides a shift in the series resonant
frequency and the parallel resonant frequency so as to more
accurately set the stopband and the passband within the first RF
communication band. The SAW resonator 178B is selectable to set the
stopband of the RF filter 162 within a second RF transmission band
of a second RF communication band and to set the passband within a
second RF receive band of the second RF communication band. The
inductance of the inductive element 184B provides a shift in the
series resonant frequency and the parallel resonant frequency so as
to more accurately set the stopband and the passband within the
second RF communication band. The SAW resonator 178C is selectable
to set the stopband of the RF filter 162 within a third RF
transmission band of a third RF communication band and to set the
passband within a third RF receive band of the third RF
communication band. The inductance of the inductive element 184C
provides a shift in the series resonant frequency and the parallel
resonant frequency so as to more accurately set the stopband and
the passband within the third RF communication band. The SAW
resonator 178D is selectable to set the stopband of the RF filter
162 within a fourth RF transmission band of a fourth RF
communication band and to set the passband within a fourth RF
receive band of the fourth RF communication band. The inductance of
the inductive element 184D provides a shift in the series resonant
frequency and the parallel resonant frequency so as to more
accurately set the stopband and the passband within the fourth RF
communication band. The SAW resonator 178E is selectable to set the
stopband of the RF filter 162 within a fifth RF transmission band
of a fifth RF communication band and to set the passband within a
fifth RF receive band of the fifth RF communication band. The
inductance of the inductive element 184E provides a shift in the
series resonant frequency and the parallel resonant frequency so as
to more accurately set the stopband and the passband within the
fifth RF communication band. The SAW resonator 178F is selectable
to set the stopband of the RF filter 162 within a sixth RF
transmission band of a sixth RF communication band and to set the
passband within a sixth RF receive band of the sixth RF
communication band. The inductance of the inductive element 184E
provides a shift in the series resonant frequency and the parallel
resonant frequency so as to more accurately set the stopband and
the passband within the sixth RF communication band.
[0145] In this embodiment, the series LC resonator 170 described
above with respect to FIG. 10A is connected in series with the
single-pole multiple-throw switch 182A. Thus, the series LC
resonator 170 is configured to be connected in series with each of
the SAW resonators 178 when a particular one of the SAW resonators
178 is selected. As mentioned above, the stopband and the passband
defined by the frequency response of the RF filter 162 are tuned
discretely by selecting one of the different SAW resonators 178.
The series LC resonator 170 shown in FIG. 10B is tunable so as to
further shift the series resonant frequency of the selected one of
the SAW resonators 178. In this manner, the series LC resonator 170
is configured to provide additional and more granular tuning of the
series resonant frequency. The transmission tuning control output
112 either represents a decoded word or has a signal level that
indicates the variable capacitance value for setting the variable
capacitance of the variable capacitive element 176. The variable
capacitive element 172 described above with respect to FIG. 10A
also is connected in shunt with the line 173 in FIG. 10B. In this
manner, the second variable capacitor is tunable so as to adjust
the frequency offset of the parallel resonant frequency from the
series resonant frequency. The receive control output 110 either
represents a decoded word or has a signal level that indicates the
variable capacitance value for setting the variable capacitance of
the variable capacitive element 172.
[0146] To select each of the SAW resonators 178, the transmission
tuning control output 112 may include a decoded word to operate the
single-pole multiple-throw switch 182A and may include a decoded
word to operate the single-pole multiple-throw switch 182B. The
decoded words indicate which of the SAW resonators 178 is to be
selected. The single-pole multiple-throw switch 182A and the
single-pole multiple-throw switch 182B are configured to select the
appropriate one of the SAW resonators 178 in response to the
decoded words in the transmission tuning control output 112. The RF
filter 162 with the SAW resonators 178 provides very good system
performance with LTE communication bands because the SAW resonators
178 have a higher quality factor performance. However, the RF
filter 160 shown in FIG. 10A may provide better performance with
respect to 3G/4G RF communication bands with larger duplex offsets
than the RF filter 162 shown in FIG. 10B.
[0147] FIG. 10C illustrates the RF filter 164. As the first RF
filter 106 (see FIG. 6A), the RF filter 164 is tunable to pass the
first RF QHRS 56 (see FIG. 6A) to the second hybrid coupler 20'
(see FIG. 6A), or, as the second RF filter 108 (see FIG. 6A) the RF
filter 164 is tunable to pass the second RF QHRS 58 (see FIG. 6A)
to the second hybrid coupler 20' (see FIG. 6A). Also, as the second
RF filter 108 (see FIG. 6B), the RF filter 164 is tunable to
reflect the first RF QHTS 60 (see FIG. 6B) back to the first hybrid
coupler 18' (see FIG. 6B), or, as the first RF filter 106 (see FIG.
6B), the RF filter 164 is tunable to reflect the second RF QHTS 62
(see FIG. 6B) back to the first hybrid coupler 18' (see FIG. 6B).
The RF filter 164 is an amalgamation of the RF filter 160 shown in
FIG. 10A and the RF filter 162 shown in FIG. 10B. In particular,
the RF filter 164 includes a switchable ground path 186 connected
in shunt between the series LC resonator 170 and the single-pole
multiple-throw switch 182A. The switchable ground path 186 includes
a switch 188. When the switch 188 is in a closed state, the SAW
resonators 178 are bypassed and the RF filter 164 operates in the
same manner as the RF filter 160 described above with respect to
FIG. 10A. However, when the switch 188 is in an open state, the RF
filter 164 operates in the same manner as the RF filter 162
described above with respect to FIG. 10B.
[0148] FIG. 10D illustrates the RF filter 166. As the first RF
filter 106 (see FIG. 6A), the RF filter 166 is tunable to pass the
first RF QHRS 56 (see FIG. 6A) to the second hybrid coupler 20'
(see FIG. 6A), or, as the second RF filter 108 (see FIG. 6A), the
RF filter 166 is tunable to pass the second RF QHRS 58 (see FIG.
6A) to the second hybrid coupler 20' (see FIG. 6A). Also, as the
second RF filter 108 (see FIG. 6B), the RF filter 166 is tunable to
reflect the first RF QHTS 60 (see FIG. 6B) back to the first hybrid
coupler 18' (see FIG. 6B), or, as the first RF filter 106 (see FIG.
6B) the RF filter 166 is tunable to reflect the second RF QHTS 62
(see FIG. 6B) back to the first hybrid coupler 18' (see FIG. 6B).
The RF filter 166 is similar to the RF filter 162 described above
with respect to FIG. 10B except that the RF filter 166 of FIG. 10D
does not have the variable capacitive element 172 connected in
shunt with respect to the line 173. Instead, the RF filter 166 has
a parallel LC resonator 190 connected in shunt between the series
LC resonator 170 and the single-pole multiple-throw switch 182A. As
such, the parallel LC resonator 190 is configured to be connected
in parallel with each of the SAW resonators 178 when one of the SAW
resonators 178 is selected. In this manner, the parallel LC
resonator 190 is tunable so as to adjust the frequency offset of
the parallel resonant frequency of the selected one of the SAW
resonators 178 from the series resonant frequency of the selected
one of the SAW resonators 178.
[0149] The parallel LC resonator 190 shown in FIG. 10D includes an
inductive element 192 and a variable capacitive element 194. The
inductive element 192 and the variable capacitive element 194 are
connected in parallel with respect to one another. The variable
capacitive element 194 has a variable capacitance and the inductive
element 192 has a fixed inductance. To tune the parallel LC
resonator 190, the receive control output 110 either represents a
decoded word or has a signal level that indicates the variable
capacitance value for setting the variable capacitance of the
variable capacitive element 194.
[0150] FIG. 10E illustrates the RF filter 168. As the first RF
filter 106 (see FIG. 6A), the RF filter 168 is tunable to pass the
first RF QHRS 56 (see FIG. 6A) to the second hybrid coupler 20'
(see FIG. 6A), or, as the second RF filter 108 (see FIG. 6A), the
RF filter 168 is tunable to pass the second RF QHRS 58 (see FIG.
6A) to the second hybrid coupler 20' (see FIG. 6A). Also, as the
second RF filter 108 (see FIG. 6B), the RF filter 168 is tunable to
reflect the first RF QHTS 60 (see FIG. 6B) back to the first hybrid
coupler 18' (see FIG. 6B), or, as the first RF filter 106 (see FIG.
6B), the RF filter 168 is tunable to reflect the second RF QHTS 62
(see FIG. 6B) back to the first hybrid coupler 18' (see FIG. 6B).
The RF filter 168 is similar to the RF filter 166 described above
with respect to FIG. 10D except that instead of having the parallel
LC resonator 190 of FIG. 10D, the RF filter 168 of FIG. 10E has a
series LC resonator 196. More specifically, the series LC resonator
196 is connected in shunt between the series LC resonator 170 and
the single-pole multiple-throw switch 182A. As such, the series LC
resonator 196 is configured to be connected in parallel with each
of the SAW resonators 178 when a selected one of the SAW resonators
178 is selected. In this manner, the series LC resonator 196 is
tunable so as to adjust the frequency offset of the parallel
resonant frequency of the selected one of the SAW resonators 178
from the series resonant frequency of the selected one of the SAW
resonators 178.
[0151] The series LC resonator 196 shown in FIG. 10E includes an
inductive element 198 and a variable capacitive element 200. The
inductive element 198 and the variable capacitive element 200 are
connected in series with respect to one another. The variable
capacitive element 200 has a variable capacitance and the inductive
element 198 has a fixed inductance. To tune the parallel LC
resonator 200, the receive control output 110 either represents a
decoded word or has a signal level that indicates the variable
capacitance value for setting the variable capacitance of the
variable capacitive element 200.
[0152] Referring now to FIG. 11A, FIG. 11A illustrates an exemplary
frequency response 202 of any one of the RF filters 160, 162, 164,
166, 168 shown in FIGS. 10A-10E. The frequency response 202 defines
a stopband 204 as a result of the series resonant frequency (SRF).
A minima 206 of the stopband 204 is set at the series resonant
frequency (SRF). Changing the series resonant frequency (SRF)
thereby shifts the stopband 204. The frequency response 202 for
each of the RF filters 160, 162, 164, 166, 168 also defines a
passband 208 where a maxima 210 of the passband 208 is set at the
parallel resonant frequency (PRF). However, the parallel resonant
frequency (PRF) is a function of the series resonant frequency
(SRF). As previously discussed, the parallel resonant frequency
(PRF) is the series resonant frequency (SRF) plus the frequency
offset (FO).
[0153] Referring now to FIGS. 11A and 11B, FIG. 11B illustrates an
RF communication channel (RFCC) having an RF receive band (RFRB)
and an RF transmission band (RFTB) separated by a duplex offset
(DO). The RF receive band (RFRB) is has a higher frequency range
than the RF transmission band (RFTB). By tuning the series resonant
frequency (SRF) to be at a frequency within the RF transmission
band (RFTB), the minima 206 is shifted and the stopband 204 is
placed within the RF transmission band (RFTB). The frequency offset
(FO) can then be adjusted to set the frequency offset (FO) to the
duplex offset (DO) of an RF communication channel (RFCC). In this
manner, the maxima 210 is shifted and the passband 208 is placed
within the RF receive band (RFRB) of the RF communication channel
(RFCC). However, the frequency offset (FO) provided by the RF
filters 160, 162, 164, 166, 168 shown in FIGS. 10A-10E cannot be
negative. Thus, the RF filters 160, 162, 164, 166, 168 are
configured to operate with the RF communication channels, like the
RF communication channel (RFCC), where the RF receive band (RFRB)
has the higher frequency range in comparison to the RF transmission
band (RFTB). Most RF communication channels defined by RF
communication specifications and/or RF communication standards have
the RF receive band (RFRB) with the higher frequency range.
However, a few RF communication channels, particularly certain RF
communication channels defined by LTE RF communication standards,
have an RF transmission band at a higher frequency range than the
RF receive band. In this case, the RF filters 160, 162, 164, 166,
168 in and of themselves would not be able to set the passband 208
within the RF receive band at a lower frequency range than the RF
transmission band. This is because the frequency offset (FO) has to
be positive and thus the passband 208 must be set at a higher
frequency range than the stopband 204. Since the stopband 204 is
tuned within the RF transmission band and the frequency offset (FO)
has to be positive, the passband 208 cannot be set within the RF
receive band at a lower frequency range than the RF transmission
band.
[0154] FIGS. 12A-12C illustrate exemplary embodiments of a tunable
RF duplexer 10C, a tunable RF duplexer 10D, and a tunable RF
duplexer 10E, respectively. Like the tunable RF duplexer 10B shown
in FIGS. 6A and 6B, the tunable RF duplexers 10C-10E include the
first RF filter 106 and the second RF filter 108. In each of the
tunable RF duplexers 10C-10E, the first RF filter 106 may be
provided as any of the RF filters 160, 162, 164, 166, 168 described
above with regard to FIGS. 10A-10E. Also, in each of the tunable RF
duplexers 10C-10E, the second RF filter 108 may be provided as any
of the RF filters 160, 162, 164, 166, 168 described above with
regard to FIGS. 10A-10E. Each of the tunable RF duplexers 10C, 10D,
and 10E is tunable to set the stopband within the RF transmission
band and to set the passband within the RF receive band whenever
the RF receive band is at a higher frequency range than the RF
transmission band. However, each of the tunable RF duplexers 10C,
10D, and 10E can also handle RF communication channels where the RF
receive band is at a lower frequency range than the RF transmission
band.
[0155] Referring now to FIG. 12A, the tunable RF duplexer 10C is
like the tunable RF duplexer 10B in FIGS. 6A and 6B, except that
the tunable RF duplexer 10C includes an RF filter circuit 22C. The
RF filter circuit 22C has the same first RF filter 106 and the same
second RF filter 108 as the RF filter circuit 22B in FIGS. 6A and
6B. However, the RF filter circuit 22C further includes a
switchable bypass path 212, a quarter-wave phase-shifting
transmission line element 214, a switchable bypass path 216, and a
quarter-wave phase-shifting transmission line element 218. The
quarter-wave phase-shifting transmission line element 214 is
connected between a line 173A and the first RF filter 106. The line
173A connects the third port 80 of the first hybrid coupler 18' to
the fifth port 84 of the second hybrid coupler 20'. In FIG. 12A,
the quarter-wave phase-shifting transmission line element 214 is
connected in series with the first RF filter 106. The switchable
bypass path 212 is connected from the line 173A to the first RF
filter 106. Accordingly, the quarter-wave phase-shifting
transmission line element 214 is connected in parallel with respect
to the switchable bypass path 212. As such, the switchable bypass
path 212 is coupled such that the quarter-wave phase-shifting
transmission line element 214 is bypassed when the switchable
bypass path 212 is closed, and is not bypassed when the switchable
bypass path 212 is open.
[0156] Additionally, the quarter-wave phase-shifting transmission
line element 218 is connected between a line 173B and the second RF
filter 108. The line 173B connects the fourth port 82 of the first
hybrid coupler 18' to the sixth port 86 of the second hybrid
coupler 20'. In FIG. 12A, the quarter-wave phase-shifting
transmission line element 218 is connected in series with the
second RF filter 108. The switchable bypass path 216 is connected
from the line 173B to the second RF filter 108. Accordingly, the
quarter-wave phase-shifting transmission line element 218 is
connected in parallel with respect to the switchable bypass path
216. As such, the switchable bypass path 216 is coupled such that
the quarter-wave phase-shifting transmission line element 218 is
bypassed when the switchable bypass path 216 is closed, and is not
bypassed when the switchable bypass path 216 is open.
[0157] When the switchable bypass path 212 and the switchable
bypass path 216 are both open, the tunable RF duplexer 10C operates
in the same manner as the tunable RF duplexer 10B described above
with respect to FIGS. 6A and 6B. However, when the switchable
bypass path 212 and the switchable bypass path 216 are both closed,
impedance transformations of the quarter-wave phase-shifting
transmission line element 214 and the quarter-wave phase-shifting
transmission line element 218 create frequency responses that can
provide duplexing when the RF receive band is at a lower frequency
range than the RF transmission band. More specifically, the
impedance transformation of the quarter-wave phase-shifting
transmission line element 214 presents a frequency response at the
line 173A that is a frequency response inversion of the frequency
response provided by the first RF filter 106. In addition, the
impedance transformation of the quarter-wave phase-shifting
transmission line element 214 218 presents a frequency response at
the line 173B that is a frequency response inversion of the
frequency response provided by the second RF filter 108. When the
switchable bypass path 212 is closed, the frequency response of the
quarter-wave phase-shifting transmission line element 214 in series
with the first RF filter 106 defines a stopband and a passband,
where the passband is at a lower frequency range than the stopband.
Similarly, when the switchable bypass path 216 is closed, the
frequency response of the quarter-wave phase-shifting transmission
line element 214 218 in series with the second RF filter 108
defines a stopband and a passband, where the passband is at a lower
frequency range than the stopband.
[0158] In this embodiment, the series resonant frequency of the
first RF filter 106 is configured to set the passband when the
switchable bypass path 212 is closed due to the frequency response
inversion. The series resonant frequency of the first RF filter 106
may thus be shifted within the RF receive band. Additionally, the
series resonant frequency of the second RF filter 108 is configured
to set the passband when the switchable bypass path 212 is closed
due to the frequency response inversion. The series resonant
frequency of the second RF filter 108 may thus be set within the RF
receive band. Thus, the series resonant frequency of the second RF
filter 108 may be shifted within the RF receive band.
[0159] The parallel resonant frequency of the first RF filter 106
sets the stopband of the first RF filter 106 when the switchable
bypass path 212 is closed and the parallel resonant frequency of
the second RF filter 108 sets the stopband of the second RF filter
108 when the switchable bypass path 216 is closed. Since the
parallel resonant frequency is equal to the series resonant
frequency plus the frequency offset, the frequency offset of the
first RF filter 106 may be adjusted so that the parallel resonant
frequency is shifted within the RF transmission band. Also, since
the parallel resonant frequency is equal to the series resonant
frequency plus the frequency offset, the frequency offset of the
second RF filter 108 may be adjusted so that the parallel resonant
frequency is shifted within the RF transmission band. In this
manner, the stopband of the first RF filter 106 is shifted within
the RF transmission band and the stopband of the second RF filter
108 is shifted within the RF transmission band. Accordingly, the
impedance transformations of the quarter-wave phase-shifting
transmission line elements 214, 218 allow for the tunable RF
duplexer 10C to provide duplexing in RF communication bands where
the RF receive band is within a lower frequency range with respect
to the RF transmission band.
[0160] Referring now to FIG. 12B, the tunable RF duplexer 10D is
like the tunable RF duplexer 10B in FIGS. 6A and 6B, except that
the tunable RF duplexer 10D includes an RF filter circuit 22D. The
RF filter circuit 22D has the first RF filter 106 and the second RF
filter 108, like the RF filter circuit 22B in FIGS. 6A and 6B.
However, the RF filter circuit 22D further includes a switchable
bypass path 220, a third RF filter 222 coupled in series between
the third port 80 of the first hybrid coupler 18' and the fifth
port 84 of the second hybrid coupler 20', a switchable bypass path
224, a fourth RF filter 226 coupled in series between the fourth
port 82 of the first hybrid coupler 18' and the sixth port 86 of
the second hybrid coupler 20', a switch 228, and a switch 230.
[0161] The switchable bypass path 220 is configured such that the
third RF filter 222 is bypassed when the switchable bypass path 220
is closed and is configured such that the third RF filter 222 is
not bypassed when the switchable bypass path 220 is open. Thus, the
third RF filter 222 does not provide filtering when the switchable
bypass path 220 is closed, and does provide filtering when the
switchable bypass path 220 is open. The switch 228 is connected
between the line 173A and the first RF filter 106, and the switch
228 is connected in series with respect to the first RF filter 106.
Thus, the first RF filter 106 does not provide filtering when the
switch 228 is open and does provide filtering when the switch 228
is closed.
[0162] Additionally, the switchable bypass path 224 is configured
such that the fourth RF filter 226 is bypassed when the switchable
bypass path 224 is closed and is configured such that the fourth RF
filter 226 is not bypassed when the switchable bypass path 224 is
open. Thus, the fourth RF filter 226 does not provide filtering
when the switchable bypass path 224 is closed, and does provide
filtering when the switchable bypass path 224 is open. The switch
230 is connected between the line 173B and the second RF filter
108, and the switch 230 is connected in series with respect to the
second RF filter 108. Thus, the second RF filter 108 does not
provide filtering when the switch 230 is open and does provide
filtering when the switch 230 is closed.
[0163] When the switchable bypass path 220, the switchable bypass
path 224, the switch 228, and the switch 230 are all closed, the
tunable RF duplexer 10D operates in the same manner as the tunable
RF duplexer 10B described above with respect to FIGS. 6A and 6B.
However, when the switchable bypass path 220, the switchable bypass
path 224, the switch 228, and the switch 230 are all open, the
third RF filter 222 and the fourth RF filter 226 provide filtering,
instead of the first RF filter 106 and the second RF filter 108.
The third RF filter 222 has a frequency response that defines a
passband and a stopband. However, unlike the first RF filter 106
and the second RF filter 108, the passband of the third RF filter
222 is at a lower frequency range than the stopband of the third RF
filter 222. Since the RF receive band is at a lower frequency range
than the RF transmission band, the third RF filter 222 is tunable
so as to set the stopband within the RF transmission band and so as
to set the passband within the RF receive band. The fourth RF
filter 226 also has a frequency response that defines a passband
and a stopband. However, unlike the first RF filter 106 and the
second RF filter 108, the passband of the fourth RF filter 226 is
at a lower frequency range than the stopband of the fourth RF
filter 226. Since the RF receive band is at the lower frequency
range in comparison to the RF transmission band, the fourth RF
filter 226 is tunable so as to set the stopband within the RF
transmission band and so as to set the passband within the RF
receive band. When the switchable bypass path 220, the switchable
bypass path 224, the switch 228, and the switch 230 are all open,
the tunable RF duplexer 10D is allowed to handle RF communication
channels with RF receive bands at lower frequency ranges than RF
transmission bands.
[0164] Referring now to FIG. 12C, the tunable RF duplexer 10E is
like the tunable RF duplexer 10B in FIGS. 6A and 6B, except that
the tunable RF duplexer 10D includes a single-pole multiple-throw
switch 232, and a single-pole multiple-throw switch 234. The
single-pole multiple-throw switch 232 is coupled to the antenna 12.
The single-pole multiple-throw switch 232 is switchable between a
first switch state and a second switch state. In the first switch
state, the single-pole multiple-throw switch 232 couples the
antenna 12 to the first port 76 of the first hybrid coupler 18' and
does not couple the antenna 12 to the seventh port 88 of the second
hybrid coupler 20'. On the other hand, in the second switch state,
the single-pole multiple-throw switch 232 couples the antenna 12 to
the seventh port 88 of the second hybrid coupler 20' and does not
couple the antenna 12 to the first port 76 of the first hybrid
coupler 18'.
[0165] With regard to the single-pole multiple-throw switch 234,
the single-pole multiple-throw switch 234 is coupled to the
impedance load 100. The single-pole multiple-throw switch 234 is
also switchable between the first switch state and the second
switch state. In the first switch state, the single-pole
multiple-throw switch 234 couples the impedance load 100 to the
seventh port 88 of the second hybrid coupler 20' and does not
couple the impedance load 100 to the first port 76 of the first
hybrid coupler 18'. On the other hand, in the second switch state,
the single-pole multiple-throw switch 234 couples the impedance
load 100 to the first port 76 of the first hybrid coupler 18' and
does not couple the impedance load 100 to the seventh port 88 of
the second hybrid coupler 20'.
[0166] When the single-pole multiple-throw switch 232 and the
single-pole multiple-throw switch 234 are both in the first switch
state, the tunable RF duplexer 10E operates in the same manner as
the tunable RF duplexer 10B described above with respect to FIGS.
6A and 6B. However, when the single-pole multiple-throw switch 232
and the single-pole multiple-throw switch 234 are both in the
second switch state, the transmission signal flow and the receive
signal flow are different and allow the tunable RF duplexer 10E to
provide duplexing when the RF receive band is in a lower frequency
range than the RF transmission band. Since the RF receive band is
at the lower frequency range in comparison to the RF transmission
band when both the single-pole multiple-throw switches 232, 234 are
in the second switch state, the tuning circuit 24B is configured to
adjust the series resonant frequency of the first RF filter 106
into the RF receive band and to adjust the frequency offset so that
the parallel resonant frequency is within the RF transmission band.
Accordingly, the tuning circuit 24B is configured to tune the
stopband of the first RF filter 106 within the RF receive band and
to tune the passband of the first RF filter 106 within the RF
transmission band.
[0167] Also, when both the single-pole multiple-throw switches 232,
234 are in the second switch state, the tuning circuit 24B is
configured to adjust the series resonant frequency of the second RF
filter 108 into the RF receive band and to adjust the frequency
offset so that the parallel resonant frequency is within the RF
transmission band. Accordingly, the tuning circuit 24B is
configured to tune the stopband of the second RF filter 108 within
the RF receive band and to tune the passband of the second RF
filter 108 within the RF transmission band. As such, the tuning
circuit 24B is configured to tune the stopband of the RF filter
circuit 22B within the RF receive band and to tune the passband of
the RF filter circuit 22B within the RF transmission band when both
the single-pole multiple-throw switches 232, 234 are in the second
switch state.
[0168] FIG. 13A illustrates the transmission signal flow of the
tunable RF duplexer 10E when the single-pole multiple-throw switch
232 and the single-pole multiple-throw switch 234 are both in the
second switch state. When both the single-pole multiple-throw
switches are in the second switch state, the tuning circuit 24B is
configured to tune the frequency response of the RF filter circuit
22B so that the stopband is within the RF receive band and the
passband is within the RF transmission band. When the single-pole
multiple-throw switch 232 is in the second switch state, the RF
transmission output signal 16 is output from the seventh port 88 to
the antenna 12. The first hybrid coupler 18' is configured to
receive the RF transmission input signal 26 at the second port 78.
Since the single-pole multiple-throw switch 234 is in the second
switch state, the first port 76 is coupled to the impedance load
100. The first port 76 of the first hybrid coupler 18' thus
isolated from the second port 78. This means that the second port
78 is substantially unresponsive to signals incident at the first
port 76, and the first port 76 is substantially unresponsive to
signals incident at the second port 78 when the single-pole
multiple-throw switch 234 is in the second switch state. As a
result, the first port 76 is substantially unresponsive to the RF
transmission input signal 26 incident at the second port 78.
[0169] The first hybrid coupler 18' is operable to split the RF
transmission input signal 26 into the first RF QHTS 60 and the
second RF QHTS 62. In this manner, the first RF QHTS 60 and the
second RF QHTS 62 have approximately the same power ratio with
respect to the RF transmission input signal 26, but have a
quadrature phase difference of approximately 90 degrees or .pi./2
radians. In the embodiment shown in FIG. 13A, the second port 78 is
phase-aligned with the fourth port 82, while the third port 80 has
a quadrature phase shift with respect to the second port 78. Thus,
the first RF QHTS 60 is approximately phase-aligned with the RF
transmission input signal 26, but there is a quadrature phase
difference between the RF transmission input signal 26 and the
second RF QHTS 62.
[0170] Note that in alternative embodiments, this may or may not be
the case. For example, there may be a phase shift between the
second port 78 and the fourth port 82. The phase shift between the
second port 78 and the third port 80 may then be equal to this
phase shift plus 90 degrees or .pi./2 radians. Accordingly, so long
as the phase difference between the first RF QHTS 60 and the second
RF QHTS 62 is about 90 degrees or .pi./2 radians, phase alignment
between the fourth port 82 and the second port 78, and between the
third port 80 and the second port 78, can vary.
[0171] The first RF QHTS 60 is output at the fourth port 82 to the
RF filter circuit 22B. Additionally, the second RF QHTS 62 is
output at the third port 80 to the RF filter circuit 22B. In this
embodiment, the RF filter circuit 22B has the second RF filter 108
and the first RF filter 106. The second RF filter 108 is coupled to
the fourth port 82 so as to receive the first RF QHTS 60 from the
first hybrid coupler 18'. The first RF filter 106 is coupled to the
third port 80 so as to receive the second RF QHTS 62 from the first
hybrid coupler 18'. The second RF filter 108 and the first RF
filter 106 each have a frequency response. The frequency response
of the RF filter circuit 22B is thus determined in accordance with
the combined effect of the independent frequency responses provided
by the second RF filter 108 and the first RF filter 106. However,
in this embodiment, the second RF filter 108 and the first RF
filter 106 are identical to one another. Furthermore, each is tuned
in accordance with a transmission tuning control output 112 from
the tuning circuit 24B. As such, the overall frequency response of
the RF filter circuit 22B is the same as the independent frequency
responses provided by the second RF filter 108 and the first RF
filter 106. Alternatively, in other embodiments, the second RF
filter 108 and the first RF filter 106 may be different and/or may
be tuned independently by the tuning circuit 24B. As such, the
different independent frequency responses from the second RF filter
108 and the first RF filter 106 may combine to determine the
overall frequency response of the RF filter circuit 22B.
[0172] Referring again to FIG. 13A, the tuning circuit 24B is
configured to tune the frequency response of the RF filter circuit
22B so that the passband includes the RF transmission band when
both the single-pole multiple-throw switches 232, 234 are in the
second switch state. The tuning circuit 24B thus shifts the
passband of the RF filter circuit 22B to include the RF
transmission band. In this manner, the RF filter circuit 22B is
operable to pass the first RF QHTS 60 and the second RF QHTS 62 to
the second hybrid coupler 20'. The manner of tuning the frequency
response may depend on the topology of the RF filter circuit 22B.
For example, the second RF filter 108 and the first RF filter 106
shown in FIG. 13A are each passive filters. Accordingly, one or
more reactive impedance components (inductive, capacitive, or both)
in each of the first and second RF filters 106, 108 may have a
variable reactive impedance level. By varying these variable
reactive impedance levels, the poles and zeros of the individual
frequency responses provided by each of the first and second RF
filters 106, 108 are adjusted. This thereby shifts the passband
and/or the stopband of the RF filter circuit 22B.
[0173] As mentioned above, the tuning circuit 24B illustrated in
FIG. 13A generates the transmission tuning control output 112 and a
receive tuning control signal 110. The variable reactive impedance
components in both the second RF filter 108 and the first RF filter
106 are set in accordance with a signal level of the transmission
tuning control output 112. In this manner, the stopband is shifted
to include the RF receive band. Similarly, reactive impedance
levels of variable reactive components in the second RF filter 108
and the first RF filter 106 are set in accordance to a signal level
of the receive tuning control signal 110. In this manner, the
stopband is set to include the RF receive band. In alternative
embodiments, the RF filter circuit 22B may include active RF
filters, SAW filters, or any other type of RF filter or combination
of RF filters that are suitable to provide a desired frequency
response. As such, the tuning circuit 24B may employ alternative
types of tuning topologies that are different from the particular
filtering topology being employed by the RF filter circuit 22B.
[0174] By placing the passband in the RF transmission band, the RF
filter circuit 22B passes the first RF QHTS 60 and the second RF
QHTS 62 to the second hybrid coupler 20'. In this particular
embodiment, the second RF filter 108 passes the first RF QHTS 60 to
the second hybrid coupler 20', while the first RF filter 106 passes
the second RF QHTS 62 to the second hybrid coupler 20'. As
mentioned above, the stopband (for example, the notch) is set in
the RF receive band.
[0175] Referring again to FIG. 13A, the second hybrid coupler 20'
receives the first RF QHTS 60 from the second RF filter 108 at the
sixth port 86. The second RF QHTS 62 is received by the second
hybrid coupler 20' from the first RF filter 106 at the fifth port
84. As discussed above, the first RF QHTS 60 and the second RF QHTS
62 have a quadrature phase difference of about 90 degrees or .pi./2
radians. Thus, for example, if the first RF QHTS 60 has a phase of
zero degrees, the second RF QHTS 62 would have a phase of
approximately 90 degrees (or .pi./2 radians). From the sixth port
86 to the eighth port 90, the second hybrid coupler 20' provides no
phase shift. Alternatively, the second hybrid coupler 20' may be
configured to provide a phase shift of .DELTA. from the sixth port
86 to the eighth port 90.
[0176] The second hybrid coupler 20' shown in FIG. 13A is
configured to provide a quadrature phase shift from the fifth port
84 to the eighth port 90. In this example, the phase shift is 90
degrees (or .pi./2 radians), and thus the second RF QHTS 62 has a
phase, as seen from the eighth port 90, of 180 degrees (note that
the second RF QHTS 62 was received with a phase of 90 degrees in
this example, and thus is seen with a phase of 180 degrees with
another phase shift of 90 degrees). Alternatively, the phase shift
from the fifth port 84 to the eighth port 90 may be .DELTA.+90
degrees (or .pi./2 radians). In any case, the phase difference
between the first RF QHTS 60 and the second RF QHTS 62 as seen from
the eighth port 90 is about 180 degrees (note that the first RF
QHTS 60 was received with a phase of zero (0) degrees and thus is
seen with a phase of zero (0) degrees at the eighth port 90).
Accordingly, the quadrature phase shift at the eighth port 90 from
the fifth port 84 results in destructive interference between the
first RF QHTS 60 and the second RF QHTS 62 at the eighth port 90.
As a result, the first RF QHTS 60 and the second RF QHTS 62 are
substantially cancelled at the eighth port 90. In this manner, the
eighth port 90 is substantially isolated from transmission signal
flow.
[0177] The second hybrid coupler 20' is configured to output the RF
transmission output signal 16 from the seventh port 88 in response
to the first RF QHTS 60 being received from the RF filter circuit
22B at the sixth port 86 and the second RF QHTS 62 being received
from the RF filter circuit 22B at the fifth port 84. In this
particular embodiment, the second hybrid coupler 20' is configured
to pass the second RF QHTS 62 from the fifth port 84 to the seventh
port 88. The second hybrid coupler 20' provides no phase shift to
the second RF QHTS 62 from the fifth port 84 to the seventh port
88. The second RF QHTS 62 is thus passed with a phase of 90 degrees
to the seventh port 88. Alternatively, the second hybrid coupler
20' may provide a phase shift of .DELTA. to the second RF QHTS 62
when passed from the fifth port 84 to the seventh port 88. The
second hybrid coupler 20' is configured to pass the first RF QHTS
60 from the sixth port 86 to the seventh port 88. The second hybrid
coupler 20' provides a quadrature phase shift to the first RF QHTS
60 at the seventh port 88. In this embodiment, the quadrature phase
shift is 90 degrees or .pi./2 radians. Alternatively, if a phase
shift of .DELTA. was provided to the second RF QHTS 62 from the
fifth port 84 to the seventh port 88, the quadrature phase shift
would be .DELTA.+90 degrees (or .pi./2 radians).
[0178] Accordingly, the first RF QHTS 60 is provided substantially
as a duplicate of the second RF QHTS 62 at the seventh port 88.
This is a result of the quadrature phase shift provided to the
first RF QHTS 60 when passed from the sixth port 86 to the seventh
port 88 (now, at the seventh port 88, the first RF QHTS 60 is
shifted to have a phase of 90 degrees, just like the second RF QHTS
62). Referring again to the example discussed previously, if the
first RF QHTS 60 has a phase of zero (0) degrees at the sixth port
86, then the first RF QHTS 60 has a phase of 90 degrees at the
seventh port 88. If the phase of the second RF QHTS 62 at the fifth
port 84 is 90 degrees, then the phase of the second RF QHTS 62 is
also 90 degrees at the seventh port 88. Accordingly, the first RF
QHTS 60 is substantially a duplicate of the second RF QHTS 62 at
the seventh port 88 because the first RF QHTS 60 and the second RF
QHTS 62 become phase-aligned at the seventh port 88. As a result,
the first RF QHTS 60 and the second RF QHTS 62 constructively
interfere at the seventh port 88 to output the RF transmission
output signal 16 from the seventh port 88. Note that since the
first RF QHTS 60 and the second RF QHTS 62 substantially cancel at
the eighth port 90 due to destructive interference, very little or
no power is transferred from the first RF QHTS 60 and the second RF
QHTS 62 to the eighth port 90. Instead most, if not all, of the
power in the first RF QHTS 60 and the second RF QHTS 62 is
transferred to the seventh port 88 and provided in the RF
transmission output signal 16. The antenna 12 is operably
associated with the seventh port 88. In this manner, the antenna 12
can radiate the RF transmission output signal 16 to transmit data
and information to external communication systems.
[0179] The first hybrid coupler 18' is thus configured to output
the first RF QHTS 60 from the fourth port 82 and the second RF QHTS
62 from the third port 80 in response to the RF transmission input
signal 26 being received at the second port 78. The RF filter
circuit 22B, however, provides isolation to the second port 78 from
the second hybrid coupler 20' and, as explained in further detail
below, from the receive signal flow. Once the first RF QHTS 60 and
the second RF QHTS 62 pass through and are filtered by the RF
filter circuit 22B, the second hybrid coupler 20' is configured to
output the RF transmission output signal 16 from the seventh port
88 in response to the first RF QHTS 60 being received from the RF
filter circuit 22B at the sixth port 86 and the second RF QHTS 62
being received from the RF filter circuit 22B at the fifth port
84.
[0180] FIG. 13B illustrates the tunable RF duplexer 10E along with
the receive signal flow. The antenna 12 intercepts the RF receive
input signal 14 as electromagnetic waves in free space. These
electromagnetic waves result in excitations within the antenna 12,
thereby converting the electromagnetic waves into the RF receive
input signal 14. The second hybrid coupler 20' is configured to
receive the RF receive input signal 14 at the seventh port 88. The
RF receive input signal 14 operates in the RF receive band within
the same RF communication band as the RF transmission input signal
26 (shown in FIG. 13A). The second hybrid coupler 20' is operable
to split the RF receive input signal 14 into the first RF QHRS 56
and the second RF QHRS 58. Since the first RF QHRS 56 and the
second RF QHRS 58 are quadrature hybrids, the first RF QHRS 56 and
the second RF QHRS 58 are approximately equal in power, but have a
quadrature phase difference of 90 degrees or .pi./2 radians. The
second hybrid coupler 20' outputs the first RF QHRS 56 from the
fifth port 84 and outputs the second RF QHRS 58 from the sixth port
86 in response to receiving the RF receive input signal 14 at the
seventh port 88.
[0181] In the embodiment illustrated in FIG. 13B, the first RF QHRS
56 is phase-aligned with the RF receive input signal 14, while the
second RF QHRS 58 has a phase difference of about 90 degrees with
respect to the RF receive input signal 14. It should be noted that
this may or may not be the case. For example, in alternative
embodiments, a phase shift of .DELTA. may be provided between the
seventh port 88 and the fifth port 84, and thus, a phase shift of
.DELTA.+90 degrees (or .pi./2 radians) would be provided between
the seventh port 88 and the sixth port 86.
[0182] The RF filter circuit 22B is operable to reflect the first
RF QHRS 56 and the second RF QHRS 58. As discussed above, the
frequency response of the RF filter circuit 22B defines the
stopband and the RF filter circuit 22B is tunable so as to shift
the stopband. For example, the stopband may be a notch that is
shiftable. The tuning circuit 24B is configured to tune the
frequency response of the RF filter circuit 22B so that the signal
bandwidth of the first RF QHRS 56 and the signal bandwidth of the
second RF QHRS 58 are each within the stopband. For instance, the
tuning circuit 24B may be configured to place the notch within the
RF receive band so that the notch is centered at the RF receive
signal frequency. In this embodiment, the tuning circuit 24B
generates the receive tuning control signal 110. Variable reactive
impedance components in both the second RF filter 108 and the first
RF filter 106 are responsive to the signal level of the receive
tuning control signal 110 so as to adjust the variable impedance
levels based on the signal level of the receive tuning control
signal 110. As a result, the notch defined by the individual
frequency response of the second RF filter 108 is shifted to
include the signal bandwidth of the second RF QHRS 58. Also, the
notch defined by the individual frequency response of the first RF
filter 106 is shifted to include the signal bandwidth of the first
RF QHRS 56. In other words, the notches defined by the individual
frequency responses of the second RF filter 108 and the first RF
filter 106 are placed in the RF receive band.
[0183] Since the tuning circuit 24B has tuned the frequency
response of the RF filter circuit 22B so that the stopband includes
the RF receive signal band, the RF filter circuit 22B blocks the
first RF QHRS 56 and the second RF QHRS 58. Accordingly, the second
port 78 is substantially isolated from the receive signal flow. The
RF filter circuit 22B then reflects the first RF QHRS 56 and the
second RF QHRS 58 back to the second hybrid coupler 20'. In the
embodiment illustrated in FIG. 13B, the second RF filter 108
reflects the second RF QHRS 58 back to the second hybrid coupler
20' at the sixth port 86. The first RF filter 106 reflects the
first RF QHRS 56 back to the second hybrid coupler 20' at the fifth
port 84.
[0184] The second hybrid coupler 20' is configured to combine the
first RF QHRS 56 and the second RF QHRS 58 into the RF receive
output signal 30. To combine the first RF QHRS 56 and the second RF
QHRS 58 into the RF receive output signal 30, the second hybrid
coupler 20' is configured to pass the second RF QHRS 58 from the
sixth port 86 to the eighth port 90. Additionally, the second
hybrid coupler is configured to pass the first RF QHRS 56 from the
fifth port 84 to the eighth port 90. However, the second hybrid
coupler 20' provides a quadrature phase shift to the first RF QHRS
56 at the eighth port 90. Thus, the first RF QHRS 56 is provided
substantially as a duplicate of the second RF QHRS 58 at the eighth
port 90. For example, if the phase of the second RF QHRS 58 is 90
degrees at the sixth port 86, the second RF QHRS 58 has a phase of
90 degrees at the eighth port 90. As such, the phase of the first
RF QHRS 56 at the fifth port 84 is approximately zero (0) degrees.
However, due to the quadrature phase shift between the fifth port
84 and the eighth port 90, the first RF QHRS 56 has a phase of
about 90 degrees at the eighth port 90. Accordingly, the first RF
QHRS 56 and the second RF QHRS 58 constructively interfere at the
eighth port 90 to output the RF receive output signal 30 from the
eighth port 90.
[0185] Also, note that the second hybrid coupler 20' is configured
such that the quadrature phase shift at the seventh port 88 results
in destructive interference between the first RF QHRS 56 and the
second RF QHRS 58. Referring again to the previous example
provided, at the seventh port 88, the first RF QHRS 56 appears to
have a phase of zero (0) degrees, but the second RF QHRS 58 appears
to have a phase of 180 degrees. As a result, the first RF QHRS 56
and the second RF QHRS 58 are substantially cancelled at the
seventh port 88. Consequently, most, if not all, of the power of
the first RF QHRS 56 and the second RF QHRS 58 is transferred to
the eighth port 90 and provided in the RF receive output signal 30.
The second hybrid coupler 20' is thus configured to output the RF
receive output signal 30 from the eighth port 90 in response to the
first RF QHRS 56 being reflected back by the RF filter circuit 22B
to the fifth port 84 and the second RF QHRS 58 being reflected back
by the RF filter circuit 22B to the sixth port 86. The
configuration of the second hybrid coupler 20' and the RF filter
circuit 22B thus provides substantial isolation between the eighth
port 90 and the seventh port 88.
[0186] As shown in FIGS. 13A and 13B, the seventh port 88 of the
second hybrid coupler 20' is configured to simultaneously receive
the RF receive input signal 14 and output the RF transmission
output signal 16. Accordingly, the RF transmission output signal 16
is output from the seventh port 88 while the RF receive input
signal 14 is being received at the seventh port 88. The tunable RF
duplexer 10E can provide this functionality because the eighth port
90 is substantially isolated from the second port 78. Accordingly,
the transmission signal flow is substantially isolated from the
receive signal flow.
[0187] FIG. 14 illustrates one embodiment of a portion of an RF
transceiver 236 having a distributed duplex filtering topology. The
RF transceiver 236 includes another embodiment of a tunable RF
duplexer 10F, an RF receive chain 238, and an RF transmission chain
240. In FIG. 14, the RF receive chain 238 and the RF transmission
chain 240 are only partially illustrated for the sake of clarity.
In particular, the RF receive chain 238 includes a low noise
amplifier (LNA) 242, which is illustrated as being within the RF
receive chain 238 in FIG. 14. Furthermore, the RF transmission
chain 240 includes an RF power amplifier 244, which is illustrated
as being within the RF transmission chain 240 in FIG. 14. The
tunable RF duplexer 10F illustrated in FIG. 14 is similar to the
tunable RF duplexer 10B described above, except that the tunable RF
duplexer 10F of FIG. 14 further includes an antenna impedance tuner
246, a third RF filter 248, a fourth RF filter 250, and a
quarter-wave phase-shifting transmission line element 252. The
first RF filter 106, the second RF filter 108, the third RF filter
248, and the fourth RF filter 250 may each be identical to one
another. The RF transceiver 236 has a distributed duplex filtering
topology, which allows each of the first RF filter 106, second the
RF filter 108, the third RF filter 248, and the fourth RF filter
250 in the tunable RF duplexer 10F shallow, but low loss.
[0188] For example, spurious emissions received at the second port
78, particularly spurious emissions within the RF receive band, can
degrade isolation performance. To help reduce spurious emissions,
the third RF filter 248 is connected in shunt with respect to the
eighth port 90 of the second hybrid coupler 20'. Just like the
first RF filter 106 and the second RF filter 108, the third RF
filter 248 is tunable and has a frequency response that defines a
passband and a stopband. The tuning circuit 24B is configured to
tune the third RF filter 248 as a slave of the first RF filter 106
and the second RF filter 108. Accordingly, the tuning circuit 24B
is operable to tune the third RF filter 248 such that the stopband
is within the RF transmission band and the passband is within the
RF receive band. In this manner, spurious emissions within the RF
transmission band at the eighth port 90 are filtered from the RF
receive output signal 30. The third RF filter 248 is shallow, but
is configured to reduce out of band emissions enough to operate the
LNA 242 linearly and reduce intermodulation products that can
impact receive sensitivity.
[0189] The LNA 242 in the RF receive chain 238 includes a linear
amplification stage 254. The linear amplification stage 254 is
operable to receive the RF receive output signal 30 from the eighth
port 90 of the second hybrid coupler 20'. The linear amplification
stage 254 is configured to amplify the RF receive output signal 30
in accordance with a linear amplification gain. Note that in FIG.
14, the RF receive output signal 30 is received by the linear
amplification stage 254 as a single-ended signal. The linear
amplification stage 254 is configured to output the RF receive
output signal 30 after amplification as a differential signal from
differential lines 256A and 256B.
[0190] The LNA 242 further includes a tunable high-selectivity
bandpass filter 258. In this embodiment, the tunable
high-selectivity bandpass filter 258 has an inductive element with
a fix inductance and a variable capacitive element with a variable
capacitance. The inductive element and the variable capacitive
element are coupled between the differential lines 256A and 256B.
The tunable high-selectivity bandpass filter 258 is tunable by
adjusting the variable capacitance of the variable capacitive
element. As a result, a passband of the tunable high-selectivity
bandpass filter 258 may be set within the RF receive band. Despite
providing greater selectivity, the tunable high-selectivity
bandpass filter 258 has a higher quality factor than the first RF
filter 106, the second RF filter 108, the third RF filter 248, and
the fourth RF filter 250, and thus may be more lossy. However, the
tunable high-selectivity bandpass filter 258 is coupled to the
differential lines 256A and 256B from the linear amplification
stage 254. Accordingly, the lossiness is not a significant
performance issue due to the amplification provided by the linear
amplification stage 254.
[0191] The LNA 242 also includes a translational filter 260 coupled
to receive the RF receive output signal 30 that is output from the
tunable high-selectivity bandpass filter 258. The translational
filter 260 is configured to translate a frequency response of an
intermediate frequency (IF) filter having a passband at an IF into
an RF frequency response with a translated passband within the RF
receive band. The translational filter 260 is self-aligned by a
local oscillator (LO) signal from an RF local oscillator. The
translational filter 260 may include an RF passive mixer along with
the IF filter. The RF passive mixer translates the frequency
response of the IF filter by mixing the RF receive output signal 30
with the LO signal, which determines an RF center frequency. The
tunable high-selectivity bandpass filter 258 significantly
increases the performance of the translational filter 260. In
essence, the RF passive mixer can create intermodulation distortion
due to mixing effects with spurious emissions at an LO frequency of
the LO signal. Since the RF passive mixer is not infinitely linear,
selectivity is added by the tunable high-selectivity bandpass
filter 258. In this manner, selectivity does not have to be
increased within the tunable RF duplexer 10F, which may result in
unacceptable insertion losses. After filtering by the translational
filter 260, the RF receive output signal 30 is output by the
translational filter 260 to a linear amplification stage 261. The
linear amplification stage 261 is configured to amplify the RF
receive output signal 30 in accordance with a linear amplification
gain, and then output the RF receive output signal 30 to the
remainder of the RF receive chain 238 for further processing.
[0192] Small reflections at the seventh port 88 due to an impedance
mismatch with the impedance load 100 can also result in distortion
at both the second port 78 and the eighth port 90. Additionally,
small reflections at the first port 76 due to an impedance mismatch
with the antenna 12 at the first port 76 can result in distortion
at both the second port 78 and the eighth port 90. To help reduce
spurious emissions, the fourth RF filter 250 and the quarter-wave
phase-shifting transmission line element 252 are connected in shunt
with respect to the second port 78 of the first hybrid coupler 18'
and in series with respect to one another. Just like the first RF
filter 106 and the second RF filter 108, the fourth RF filter 250
is tunable and has a frequency response that defines a passband and
a stopband. The tuning circuit 24B is configured to tune the fourth
RF filter 250 as a slave of the first RF filter 106 and the second
RF filter 108. However, the quarter-wave phase-shifting
transmission line element 252 provides a frequency response
inversion to a frequency response of the fourth RF filter 250. As
such, the stopband of the quarter-wave phase-shifting transmission
line element 252 in combination with the fourth RF filter 250 is
provided within the RF receive band, while the passband is provided
within the RF transmission band. Accordingly, the tuning circuit
24B is operable to tune the fourth RF filter 250 such that the
stopband is within the RF receive band and the passband is within
the RF transmission band. In this manner, spurious emissions within
the RF receive band are filtered by the fourth RF filter 250 prior
to the RF transmission input signal 26 being received at the second
port 78. Furthermore, spurious emissions that are reflected to the
second port 78 are also filtered by the quarter-wave phase-shifting
transmission line element 252 in combination with the fourth RF
filter 250.
[0193] The RF transmission input signal 26 is received at the
second port 78 from the RF power amplifier 244, which is in the RF
transmission chain 240. The RF power amplifier 244 includes a
plurality of RF amplifier stages (referred to generically as
element 262, and specifically as elements 262A-262B) coupled in
cascode. Accordingly, each of the plurality of RF amplifier stages
262 is operable to provide amplification to the RF transmission
input signal 26. In other words, by being coupled in cascode, the
RF amplifier stages 262 provide amplification to the RF
transmission input signal 26 in sequence.
[0194] The RF power amplifier 244 shown in FIG. 14 has a power
amplification circuit 264. The power amplification circuit 264 has
an initial RF amplifier stage 262A and a final RF amplifier stage
262B. However, other embodiments of the RF power amplifier 244 may
include any number of RF amplifier stages 262 greater than or equal
to two (2). The initial RF amplifier stage 262A is the RF amplifier
stage 262 at a beginning of the sequence. The final RF amplifier
stage 262B is the RF amplifier stage 262 at an end of the sequence.
Since at least two RF amplifier stages 262 are needed to provide
cascoded RF amplifier stages 262, the RF power amplifier 244
includes at least the initial RF amplifier stage 262A and the final
RF amplifier stage 262B. However, the number of RF amplifier stages
262 may be any integer greater than or equal to two (2). As such,
there may be any number of intermediate RF amplifier stages,
coupled in cascode between the initial RF amplifier stage 262A and
the final RF amplifier stage 262B. Since the RF amplifier stages
262 are coupled in cascode, the RF amplifier stages 262 provide
amplification to the RF transmission input signal 26 in sequence.
Accordingly, the initial RF amplifier stage 262 initially provides
amplification to the RF transmission input signal 26 in accordance
with an amplifier gain G.sub.initial. Once the RF transmission
input signal 26 is amplified by the initial RF amplifier stage 262A
in accordance with the amplifier gain G.sub.initial, the final RF
amplifier stage 262B amplifies the RF transmission input signal 26
in accordance to an amplifier gain G.sub.final. As such, an
aggregated amplifier gain of the plurality of RF amplifier stages
262 as a whole may be described as G.sub.initial*G.sub.final.
[0195] The RF power amplifier 244 shown in FIG. 14 is operable to
receive the RF transmission input signal 26 from upstream RF
circuitry, prior to amplification. As shown in FIG. 14, an RF
filter 266A is coupled to receive the RF transmission input signal
26. The RF filter 266A has a frequency response that defines a
stopband, such as a notch. The RF filter 266A is tunable so as to
provide the stopband within the RF receive band. In this manner,
spurious emissions within the RF receive band from the upstream RF
circuitry are reduced. Once the RF filter 266A has filtered the RF
transmission input signal 26, the initial RF amplifier stage 262A
receives the RF transmission input signal 26 and provides
amplification to the RF transmission input signal 26 in accordance
with the amplifier gain G.sub.initial.
[0196] The RF power amplifier 244 also includes an RF filter 266B
coupled in series between the initial RF amplifier stage 262A and
the final RF amplifier stage 262B. In other embodiments where the
number of RF amplifier stages is greater than two (2), there may be
other RF filters, like the RF filter 266B, coupled in series
between the RF amplifier stages. The RF filter 266B has a frequency
response that defines a stopband, such as a notch. The RF filter
266B is tunable so as to provide the stopband within the RF receive
band. In this manner, spurious emissions within the RF receive band
from the initial RF amplifier stage 262A are reduced. Thus, by
distributing filtering of spurious emissions within the RF receive
band throughout the power amplification circuit 264, the tunable RF
duplexer 10F can have less selectivity and lower insertion losses.
This is important, since the power amplification circuit 264 may be
connected to an RF power converter 268. The RF power converter 268
is configured to generate a supply voltage from a power source
voltage in order to power amplification by one or more of the RF
amplifier stages 262. The RF power converter 268 may include a
switching circuit in order to generate a pulsed output voltage from
the power source voltage and an RF filter that converts the power
source voltage into the supply voltage. While such systems are
power efficient, switching circuits can generate high levels of
spurious emissions. Distributing duplex filtering throughout the
power amplification circuit 264 allows the tunable RF duplexer 10F
to have lower insertion losses while maintaining adequate isolation
between the receive and transmission signal flows.
[0197] As mentioned above, small reflections at the first port 76
due to an impedance mismatch with the antenna 12 at the first port
76 can result in distortion at both the second port 78 and the
eighth port 90. Thus, the antenna impedance tuner 246 is coupled
between the antenna 12 and the first port 76. Since the RF
transmission output signal 16 is in the RF transmission band, the
impedance of the antenna 12 may result in a portion of the RF
transmission output signal 16 being reflected back to the first
port 76. This not only would degrade the RF transmission output
signal 16, but would also degrade the isolation between the receive
signal flow and the eighth port 90. The antenna impedance tuner 246
is tunable so as to reduce reflections from the antenna 12 to the
first port 76. More specifically, an impedance of the antenna 12
may be tuned so as to provide impedance matching between the first
port 76 and the antenna 12.
[0198] As shown in FIG. 14, a digital calibration circuit 270 is
coupled to the tunable RF duplexer 10F. The digital calibration
circuit 270 is configured to calibrate the tunable RF duplexer 10F.
With regard to the first hybrid coupler 18' and the second hybrid
coupler 20', the digital calibration circuit 270 performs a hybrid
calibration routine for each of the RF communication bands. During
the hybrid calibration routine, the first RF filter 106, the second
RF filter 108, the third RF filter 248, and the fourth RF filter
250 are set in a neutral state so as to be fully transparent within
both the RF transmission band and the RF receive band. An RF tuning
signal operating within the RF transmission band is then injected
into the second port 78. Power for the RF tuning signal is set to
be at least 20 dB less than maximum power so that a detector in the
digital calibration circuit 270 is not burned. The power at the
seventh port 88 is then measured and the digital calibration
circuit runs a gradient search for maximum power at the seventh
port 88 by tuning the first hybrid coupler 18' and the second
hybrid coupler 20'. Calibration data for the transmission frequency
band is then stored and a correction for the receive frequency band
is calculated for both the first hybrid coupler 18' and the second
hybrid coupler 20'. In receive noise critical scenarios, the first
hybrid coupler 18' and the second hybrid coupler 20' are tuned in
accordance with the correction. In case of transmission insertion
loss or transmission leakage issues, the first hybrid coupler 18'
and the second hybrid coupler 20' use the calibration for the RF
transmission band.
[0199] Once the hybrid calibration routine is completed, a filter
calibration routine is performed. Initially, the variable
capacitance of the variable capacitive element 176 (see FIGS.
10A-10E) is adjusted until minimum power is detected at the seventh
port 88. Alternatively the forward power between the first port 76
and the antenna impedance tuner 246 or between the antenna
impedance tuner 246 and the antenna 12 is used to determine a notch
frequency for the RF transmission band. In that case, the goal is
max power at the forward coupled output. Once the appropriate
values are determined, the optimal tuning setting is copied to the
RF receive band (.lamda./4 inverted RF transmission band notch) at
the transmission side and the RF transmission band notch at the
receive band side in front of the LNA 242.
[0200] Those skilled in the art will recognize improvements and
modifications to the embodiments of the present disclosure. All
such improvements and modifications are considered within the scope
of the concepts disclosed herein and the claims that follow.
* * * * *